My body's nipples just enlarged out of nowhere with a very big lump under them. This annoys me because I'm shy to take off my shirt in front of my friends or family. They also can be seen through my shirt. What should I do to fix this?
It is a normal part of growing up. Your body is storing fat to get ready for your growth spurt and the extra fat is making your nipples stick out. As you get done growing, the bulging will go down. Meanwhile, you'll just have to accept that this is way you'll be for a few years.
One thing you can do is wear a tight tee-shirt or sleeveless undershirt under your shirt. It will spread the bulges out so they won't be so noticeable under your shirt.