Breast growing rapidly and hurt (please look)

About a month ago

Today. Didn't tighten the bikini at all. My boobs have been hurting really badly and feel really tight and heavy. They also feel lumpy underneath. Not like breast cancer, but the tissue is hard and lumpy. Why are my boobs growing like this when I'm 19? I also have taken two pregnancy test a week apart and they've been negative both times. I've also been having period cramps but no periods. My periods are irregular because I'm on the implant and have been for two years now.