Breast Swollen on one side?!

Breast Swollen on one side?

I woke up this morning with pain in my left breast. I went to take a shower and noticed that it's gotten bigger overnight as well. Nothing extremely dramatic, and possibly most people wouldn't have noticed had they seen it, but I definitely notice a difference, even if it isn't dramatic. It's a lot more sensitive than the right breast, and I noticed that the gland seems a lot bigger. I have no idea what is going on, and I'm even a little uncomfortable to talk to anyone about it, but it's kind of scaring me, especially since it's just one side. Does anyone know what this is?

1 week ago
Oh I forgot one detail, I'm 20 years old by the way. I don't know if that helps or not.

1 week ago
Another detail I forgot to mention... I'm definitely NOT pregnant. That's impossible, being as I'm a virging. It's got to be something else then.

It could be anything. If your boyfriend was too rough. ;) Maybe your breasts are still growing! Just keep an eye on it. Do a self- check and see if you find any lumps or anything different or weird. If you do, then go to the doctor and have it checked out. When I'm on my period my breasts get swollen, maybe it's that? Or maybe you just slept on it wrong!