Hey, Congrats and welcome to AM
I just recently posted something similar to this. I gave birth on June 11, 2010 to a beautiful baby girl. I too used to be active and fit but closer to my pregnancy I had some complications. I was put on bed rest and thats when it all started. I also gained weight after birth and just completely let myself go.
I took the advice of Rosie (post above) and it has been great.
I began with 5lb dumbbells following the exercises in Rosie "3 keys to fat loss" for beginners. I am now up to 10lbs and am feeling great. I eat healthier and am motivated and determined.
Hang in there! I suggest you read the "3 keys of fat loss" and also a book "burn the fat, feed the muscle." I could provide you with a free pdf file if you are interested.