Stretch marks and sagging 😞

When I was younger I used to have small boobs and was really self conscious about it but then when I was 17 (I'm 19 now) I got pregnant and my boobs got really big. I went from a B or C to between a D and DD. I loved it so much because I've always wanted big boobs. The only problem is that now i have stretch marks all over my boobs and after i had my son and stopped breast feeding him my boobs got super saggy. Still size D-DD but just saggy. Does anyone know how to get rid of the stretch marks and sagging? Im only 19 years old but because of the way they look now I'm too self conscious to go out without a bra or to wear a strapless shirt.. I just want to be able to feel confident again.