Something wrong?

Really need advice.  I stopped birth control in Feb. Had my first period after that March 14. (4 days later than expected) My period is due in 6 days if going by last cycle. This morning I woke up and after peeing noticed brown / light pink on the toilet paper.  Very light but noticeable.  Is there a chance my period is coming early? I had sex last night. It lasted longer than normal but I had no pain with it. I am scared.  Before stopping my birthcontol my period came around the 8th of the month. I don't know. Just concerned.  Having lower back pain / mild cramps.  Help! Thanks you.