Pregnancy can do it, but I wouldn't recommend pregnancy for that reason only.
Gaining weight will do it, though it's not healthy to do that. Some people find that birth control makes their boobs bigger, but it can also have the opposite effect depending on the pill or only cause it because of weight gain.
It's usually better to find the perfection in what you view as an imperfection and accept yourself where you're at. You'll find that if it is a self-image issue simply getting bigger boobs isn't going to deal with the root issue.
Trust me, they're not good. I would love to give you some of mine. I can't wear cute tank tops or sundresses or anything and forget about sleeping on my stomach. It's better to have smaller ones. I was. 36c in high school but then I gained weight and now I'm like a 46h. It stinks. I would get a reduction but I have heard too many horror stories so I'm trying to lose weight instead, very difficult.
I can also attest to how different a person's whole image can be when the boobal region grows, and I don't mean sexy. I got bigger after pregnancy and nursing, and where overall I used to look slim and lithe, now I look like the Queen Mary, prowing through the waves. Very matronly. People tend to see you as fat or thin depending on the chest, it's the first visual, and no matter that my hips didn't grow at all (they didn't), I look much more stodgy. Not to say you should not wish for what you want, but just that sometimes it's not a blessing. I looked athletic and slim, before, and lithe and young. I used to look like Duchess Kate, now I just look like the Queen.