Im having a weight issue and need some advice... help???

This is kinda tricky, I just had a baby 6months ago and had a c-section, a month later had my gall bladder removed. Bc of all this I was taken off work for 3 months, and the pounds keep adding on. I am not lazy and work over 40 hours a week as a waitress in a fast paced restaurant. I also have a under active thyroid and a slow metabolism, and poly cystic ovaries. I dont eat very much like 3 meals a day. Nothing seems to help me lose weight. I am also on a birth control named LO/OVRAL 28. before I was pregnant I was on a birth control named ortho tri cyclen. It made my periods regular and the pounds (and fat) drop right off. Maybe someone has had the same problem as me and knows a effective exercise I can do with minimal strain to my back( bc its bad)?!?! I have always been kinda big, but my stomach is alot bigger than the rest of my body. My legs are rock hard and so is my , My arms are a little big as is my face, my my stomach look out of proportion. Any help?