One Sore Nipple :/

Ok I have one sore (left) nipple. My cycle is 18 days late. I get my cycles at the end of each month. So my cycle for October came on the 31 and ended sept 7 . Well I haven't gotten the one for September yet and it's October 18th. I took a ept and it was negative. I had an incident where the whole condom came off inside of me. No sperm in it maybe a little Precum  :/