Help me plzzz

I’m on day 18 of my cycle. I have been dealing with extremely painful boobs and nipples. It’s gotten better but my nipples are hard constantly and won’t go down and it feels as though my boobs are huge. I’m not pregnant and haven’t had sex (that’s when I lost my virginity) for like 2 months so that’s not the issue. I am on the birth control pill. I wondering if my body is just changing?