I've copied this from the low carb forum that I use, www.low-carbdiet.co.uk/ :
The weight loss has stopped what am I doing wrong?
Everyone experiences a slowing down or stopping of weight loss at some point in their diet. Listed below are a few things that may help you understand why and what you can do to get moving again.
Water.
Water is essential to weight loss for those who eat low-carb. The minimum consumed in a day should be
Weight-----Litres
140lbs-----2.5
160lbs-----3.0
180lbs-----3.0
200lbs-----3.5
220lbs-----3.5
240lbs-----4.0
260lbs-----4.5
280lbs-----4.5
300lbs-----5.0
320lbs-----5.5
340lbs-----5.5
360lbs-----6.0
380lbs-----6.5
400lbs-----6.5
High levels of ketones in the blood stream can lead to a reduction in ketone production, therefore being well hydrated could aid in keeping the levels low and ketone production ongoing. Consuming enough water can have many other positive side effects: aids your kidneys with the processing of protein, reduces the retention of water, helps with preventing constipation, and reduces the levels of ketones released by your breath, which in-turn will reduce breath odour.
Citric acid.
Citric acid, a common ingredient in diet drinks, can stall weight loss for some lowcarbers. If you are sensitive to this ingredient it can slow you down.
Caffeine.
Many lowcarbers drink caffeine and still lose weight. You may want to wean yourself off caffeine to see if it helps. In Atkins' book, The New Diet Revolution, it says that you aren't allowed caffeine because it triggers an insulin response, but that information has since been found to be incorrect. The insulin response that Atkins saw in his patients was more likely due to citric acid. Do keep in mind that one cup of coffee can have roughly .6g of carbs, so make sure to add those into your daily carb allowance.
Dairy
Dairy can be a problem for some people. If you experience slow or stalled weight loss try reducing or eliminating dairy, especially cheese. Some have found better results by cutting all dairy. Although cheese is allowed on lowcarb plans it does seem to effect weight loss if consumed in high quantities.
Nitrites
Nitrites - found in processed meats like hot dogs and bacon can cause problems for some, you may want to monitor their effect.
Alcohol
This is an area that seems to vary a great deal between individuals. While it is true that many alcohol products contain few carbs, alcohol itself is a fuel source. The body will choose to burn alcohol before any other source of fuel. However, many people have reported that they are able to consume moderate amounts of alcohol while on low-carb without having any problems. As most people are already aware, alcohol has a depressant effect which lowers inhibitions, including those that could stop you from overeating and making poor food choices.
Menstrual Cycle
Many women find that their progress is affected by their menstrual cycle. After a few months, you will have an idea of how your cycle affects weight loss, and you will be able to take it into account when measuring your losses. People have noted the following interactions between low carb eating and the menstrual cycle in women include: heightened carb cravings in the second half of the cycle, ketosis levels dropping or disappearing altogether, differences in the amount and severity of cramps, changes in the heaviness and timing of the cycle. Additionally it has been noted that a low-carb diet is very helpful to women with PCOS.
Protein
Although getting adequate protein is of vital importance on a low-carb plan, taking in too much protein can also be a problem. You will need enough dietary protein to avoid any muscle loss and to produce some necessary glucose. Protein is converted to glucose at a rate of roughly 58%. Therefore, too much protein can produce too much glucose. If you are having problems with staying in ketosis (or getting into ketosis), you may need to track your intake of protein and then make adjustments. It is highly recommended that you don't restrict your intake of protein in the initial adaptation stage of starting a low-carb plan.
Glycerine
One of the recurring issues of stalls and labelling discrepancies regards many of the low-carb protein bars currently on the market. While the true carb count of the bars is low, most of these bars contain glycerine. Although glycerine is not a carb, it can be metabolised like a carb by some individuals. Additionally, it can cause muscle cells to hold water, hence its use by some athletes.
Prescribed Medicines
There are a number of medicines that can interfere with weight loss, the worst offenders are the psychotropic drugs; phenothiazines, tranquillisers, anti-depressants, etc. The next are hormones such as oestrogen, prednisolone and other steroids. Many anti-arthritic drugs especially NSAIDS, diuretics and to a lesser degree other cardiovascular medications. You cannot stop these medications! Atkins suggests that you can gradually replace the drug with diet and suitable supplements. Do not stop medications without consulting your Doctor!!!
Hormonal Balance
A significant percentage of people, who have difficulty losing weight, have an under-active thyroid. The typical symptoms are; mental and physical slowness, lethargy, memory loss, heavy periods, a hoarse voice, increased weight and intolerance of the cold. The eyes may become swollen, the skin dry, and the hair ?lifeless?. Constipation is also common. You can ask your doctor for a thyroid function test if you think you may have this condition.