You are on a powerful, controversial (debates over its black-box warning) blood sugar regulation medicine and you are looking to your diet as reasons for symptoms?
Always carefully read the package insert of any medication you take, and search the internet for reported side effects.
For example, some Avandia side effects are:
nausea, stomach pain
increased thirst and hunger
diarrhea
unusual tiredness or weakness
EDIT: thinking more about this, Avandia's controversial side effect is the fluid retention and edema that may lead to heart issues. Wondering if some of that 20 pound loss was you having more water to shed than the average 220 person?
The list of medications which can interfere with weight loss is long; any hormones for almost any reason, and any of the blood sugar/diabetes ones.
Avandia is usually not one that would cause a hypo, but it could "be overkill" as you write and also causing the tiredness, trouble sleeping, stomach issues, etc.
http://www.drugs.com/sfx/avandia-side-effects.html
Always talk with your doctor before changing any meds, but good for you starting a low carb diet for PCOS. I have read/heard interviews about using a Paleo diet for PCOS/infertility. Low Carb plus a stronger focus on nutrient -dense foods and avoiding toxins in our diet. Hope you feel better and Wishing you all the best,