Potatoes- the thing to remember about them is they are a gut irritant to many people, although skinless ones, and baby new potato tend to be better tolerated.
I am one of those potato sensitives, and the major effect is overwhelming fatigue within a couple of hours of eating them, and muscle and joint pains a few hours after that, which last a couple of days. I also get the same with other nightshades such as chilli, sweet peppers and tomato but limited amounts are ok now and again.
I never would have realised that (and other food sensitivities), if I hadn't removed absolutely ALL grains, and starchy veg for a couple of months - with reintroductions of foods after that it was a lot easier to see which foods were causing problems. On a standard diet, I was so fatigued, pained and ill all the that it was difficult to point the finger at any individual food with much certainty, other than my obvious egg yolk allergy and the strong conviction that gluten grains were causing me more problems than anything else (which was true).
Unfortunately, after a period of "clean" eating, if you get a little lax and eat something that you react to, potato, gluten, whatever, you could get a much stronger reaction than before - the trick is to try and remember what you've eaten (or eaten a lot more of) in the 1-2 days before. There are an awful lot of people who never know gluten (for example) is making them ill until they stop eating it for a few weeks for something like "whole30".
White rice is regarded a quite benign, ie not actually good for you, potatoes less so, you need to be sure you are not reacting to them. Try this little experiment, eat a simple dinner with only a couple of ingredients - a large portion of potato, and some grilled chicken breast, maybe a few salad leaves with no dressing.
If you feel bloated/lead weight in your stomach, very sleepy after a couple of hours, joint or muscle pain within about 18 hours, then potatoes are not a good choice for you!
A useful indicator of which foods you may be allergic/intolerant to, are cheaply available (less than £50) online blood tests (easy to do, but several steps to follow). These test for antibodies for common food allergens.
I did one of these tests several week after starting grain free, paleo eating. I showed a strong antibody response to all of the grains including maize and rice, and potatoes, egg, and small reaction to pepper, cashews and shellfish... A reaction does not mean you should never eat that food again, but that you should remove and reintroduce after a few week to see what happens, and that maybe you can eat that food occasional but daily - it's trial and error.
I found the antibody tests to be a very useful pointer and tool for finding which things were making me feel bloody awful! I'd recommend one that's testing at least 50 common food reactions.
With paleo and primal woe, it is very important to remember that the adding back in of more carbohydrate to the diet is for AFTER weight loss and metabolic issues have been resolved, and in line with the activity levels of the individual. Eating too many now will slow weight loss but also slow any health gains you may get from eating this way.
After initial carb flu, lack of carbs should not make you feel fatigued, if you are eating plenty of fat and protein, I think it's more likely to be illness or a food reaction - but of course some people do better on a little bit more carb, some on less. It is likely that for most people, they should not be going over 50-70g carb per day for weight loss. Many are happiest at between 20-50g per day- which should give good weight loss but is not very very low carb.