WHAT COULD THIS BE?!?

my partner and I had sex last month on my fertile days, I was fertile March 21st-27th, then this month on april 4th-6th i started spotting brownish/pinkish blood to light to fill a tampon or pad it was only there when i wiped.. i was supposed to start my period on april 9th but it never came. 3 days later i decided to take a pregnancy test but it came back negative. i am now 7 days late and beyond confused i usually have a 32 day cycle. I've never spotted for only 2 days and im never early if anything im usually a day or 2 late. this is how light the blood was.. any ideas what i should do or has any one been in the same position? what was your out come if so?