Hi P.,
I have a 7-month old boy and have been taking the mini pill since he was about 7 or 8 weeks old, I think. I never experienced any side-effects, although I never did in the past with other birth control pills either. I've heard that it can affect milk supply in some woman, especially those who had problems with supply from the beginning. But if you never had problems with your supply, I wouldn't worry about this. I haven't heard of anyone gaining/losing weight on it. In fact, the side-effects seem minimal, in my experience. I have a lot of friends who take the pill too.
It's normal to have zero sex-drive after delivery, especially if breast-feeding! Your body produces zero estrogen when breast-feeding, which partically contributes to this. Your sex-drive will return. I wouldn't worry too much.
Good luck!
D.