ok, this is embarrassing and i cannot believe i am writing this in a public forum! lol.
i had the same issue. i was a C cup before getting pregnant with my daughter. within my first 4 months of pregnancy, i swelled up to a DD. after having her and while i was nursing i sat at a D. i stayed a D while pregnant with my son and while nursing him. then i weaned him and OH MY GOD. they shriveled away to nothing! i was a floppy B all of a sudden and it depressed me to death. i am not sure if you watch family guy, but i was exactly what they talk about on there, "full blown fried egg nailed to a board"
as embarrassing as it is, i started to take a breast enhancement supplement online. I looked at a lot of different ones and finally settled on breast success. the label looks terrible, and the name is equally bad. but it really DOES help. i didnt have the big dramatic results like they have in testimonials like, "i went up 2 cup sizes in 4 months!" etc. but i did got up a cup size and it at least helped my boobs poof back up and not look so deflated. I am back to the C i was before having kids, and pretty comparable to how they looked before i ever got pregnant (minus the stretch marks of course!)
oh, and i bought mine on ebay, its a lot cheaper! lol. also, one month doesnt show much difference, its the second and third month that you start to see the difference, so avoid the frustration and get a pack of 2 or 3 bottles!