Love the 'tit bits'
I found that getting a really good bra for support and getting fitted for my post baby boobs was the main thing. Doing push ups (from the knees) has firmed my muscles on my chest.
Also try lying on your back on a bench or the bed feet flat on the floor and using dumbells or a couple of tins of food lift in each hand - start at your chest then straighten your arms up try to keep your back as straigth as and don't put the wieghts over your belly or head.
You probably could ask your gp for some other exercises and the correct way to do them too
hope that helps
Rachel, QLD mum of Zaki 21 months