please help

although this might be tmi, please bear eith me for a bit.
I wear bras a lot cuz I'm uncomfortable with my breast just hanging but yesterday, I didn't wear a bra for the whole day. Last night my nipple started hurting and it wont go soft. I've only woken up a few minutes ago and have been searching for stuffs regarding my issue. There is a lump behind my nipple. my period ended like 3 days ago and I don't know if this is normal. sure it ain't. it's really painful cuz it's only on one side and I did book an appointment to see a doctor in like a few hours. It's just really painful like it's swollen. I haven't done some sexual activities so I'm so confused why it got so hard it's painful.