Firstly, it's very common on weeks 3 and 4 of a low carb diet for the weight loss to stop or slow down (sometimes people gain as well), so don't worry on that front. If you've lost 3kg, that's great! That's almost half a stone, so well done.
However, looking at what you've eaten today:
Today I've had: egg muffins - eggs, cream, spinach, feta, salt and pepper
Perfect low carb food. I love these!
Shed load of olives
Great - also good low carb food
Babybel cheese
Karl Kari (peanut butter but otherwise I think low carb although I can't find banana flower on any carb list!)
I have no idea what you mean - what is this?! Peanut butter can be quite carby, so check the label on the jar. Did you mean banana 'flower' or 'flour'?! According to this site, if it's banana flour, this will be too carby
One cup of tea with low fat milk (is this enough to cause an issue? I hate tea with full fat milk)
If it's only one cup, then it shouldn't be a problem - but milk can quickly become carby, especially low fat milk.
Two diet cokes (zero carb but do these trigger something)
The jury is out on artificial sweeteners, but some say that they provoke an insulin spike similar to that of sugar, so can impede weight loss. Best avoided, to be honest.
I did have a fair amount of vodka lime and soda on Thursday but I still lost weight that day. I was also eating nuts which I've just realised is a no no. Is it possible the alcohol had a delayed effect?
Alcohol is the easiest form of fuel for the body, so all the time you've been drinking, your body will be burning this rather than fat or carbs. You will probably have lost weight the next day through dehydration.
Looking at this overall, it could be that you're just eating too many carbs - you might also want to keep an eye on how much dairy that you're having. And definitely avoid the artificial sweeteners.