one way i gauge appropriate calorie burning for myself is by baby wearing -- if we are on a walk, he rides in an ergo backpack, around the house he often hangs out in the sling. this very much is a work out without much extra effort, and my son loves it! my arms, back, legs, and especially butt benefit from this. you will be working calories off, but it will be functional and find it a very integrated and balanced way of working with your body. also, i have noticed that myself and many other mothers really appreciate dairy fat, and maybe this is a milk-helper? (i don't know). an IUD may be your best non-disciplinary form of birth control, it works simply because it is a foreign object in your body, but ANY hormone birth control will definitely reduce your milk supply. also, if your child is nursing at night, this will help keep your supply up. frequency of nursing affects milk supply very much, so maybe consider pumping just to get more production. also, the fat will eventually burn if you continue nursing! at five months out, its okay to just relax! your body is burning calories by nursing!
my son is 18 month old, still an avid nurser, at did not take much solid food until 11 months. as a consequence of this and simply wearing him, my muscle tone developed alot and i weigh less than i did before becoming pregnant.
good luck!