okay so on Wednesday the 11th my period started , it was normal ,5 day and everything. It ended on the 15th

I had sex on the 16th and that same day I took a plan b pill since my boyfriend most likely did not finish outside.

This morning I noticed some CM that looks exactly like the beginning of a period and just now (2:00 am) I get up to pee and I see red, no discharge but it looks as if my period is starting again.. what could it be?? Please help!

Also, took a pregnancy test and it’s negative, I feel like I HAVE been stressed due to my job but I honestly don’t know what it could be.