Loose skin

I have loose breast skin and it makes me miserable. I went from I lost 45 pounds when I was 17 bringing my cup size from a D to B. My once perky boobs were all of a sudden small and kind of saggy. I've hated it but dealt with it but now I've gained weight. I'm trying to lose it but I'm terrified of being left with more loose skin. I know you can't do much for loose skin without surgery but are there exercises or something specifically I can do to firm up my chest enough for the loose skin to not be as much of a problem?