I Had Sex On March 18th On The Last Day

I had sex on March 18th on the last day of my period. So far I've had a period in April and in May. Three days ago I took a pregnancy test and it was negative. However, today is the last day of my May ovulation and Im having spotting which I never experienced before. I got off birth control about 1 to 2 months ago, so is this why Im bleeding? I also think that my lower stomach is getting bigger and my cervix isnt getting as hard when it's supposed to and as soft and high as it should be for ovulation.