Hey,
i'm 21 years old too and I discovered a lump in my left breast when I was 19. It did not hurt me, but I could feel it moving around a bit when I touched it, and after several months, it increased in size.
It was a completely benign (non-cancerous) tumor called a fibroid adenoma and I had it removed, no problem. :d
i don't know if this is what you have, but what I am saying is, do not be concerned yet, just go get it checked out again.
Also, there is a great health site I use for my health information called health site guide. There is a whole mini-site on breast cancer that can be accessed from the home page. I suggest giving it a look to see if you can better place your symptons.
Hope this helps. Let me know!