^^^Hun, your mom is one of the very very lucky ones, and you probably will be too!^
It all depends on your genes, and if you don't have the greatest genes and have great collagen in your skin, trust me there is NOTHING out there except plastic surgery to make things the same as before. I'm pregnant with twins, 36 weeks, and I started getting stretch marks at 30 weeks. Now they are from my pubic bone to above my belly button. I've spent $$$$$ on trying to prevent them since I found out I was pregnant. I used cellex-c on my belly to help with collagen, used expensive belly cream, dry skin brush for exfoliation, used glycolic acid cream to remove dead skin, used all natural oils, shea butter and cocoa butter! Also took fish oil, extra vitamin C, collagen pills, extra zinc, plus a homeopathic for stretching!!!! I remember my mom's belly was also very scarred, and both sisters got stretch marks. Now, their belly's may not be what they were before, but they aren't saggy, they did tone back up. Hope mine does! What I'm saying is it's not impossible to avoid saggy skin and stretch marks, but MOST women get it. I tried everything possible and still got them
Everyone is very different, you might get it, you might not, either way it's not your fault what you were dealt, it's luck of the draw. You just gotta go with the flow. I was so upset, and honestly still am about all the stretch marks...but then I think...oh well, I wasn't exactly running around in a bikini before!!!