I need to gain and tone, help please.

I am trying to gain weight and get back into shape. Any ideas are welcome. I have been pregnant 5 times and had 4 live births, I breast fed all 4. Now I have the flat and saggy breasts of a 90 year old woman. I am about to be 24, I want my body back... Breast feeding took me from 137 to 70 pounds and now I am back up to 82 pounds, what can I do? I have had little  progress on my journey to gain my body back, I eat but maybe I am eating the wrong things...