You have youth on your side, so your skin might tighten back up some on it's own over time, and strength training combined with healthy diet would probably help the appearance of the loose skin by firming up the tissue underneath. Unfortunately, some of the havoc wreaked on the body from pregnancy can't be undone, short of plastic surgery. I have the same issue to some extent, and it's been 13 years since I was pregnant. It definitely improved with some time (I was 21 when I had my daughter), but when I feel any insecurity creeping in, I just remember that those imperfections are like badges of honor... I earned them and they were well worth it!