I started my last period march 26. I was due for it April 25, I usually have 30-31 day cycles. I never got my period. I had sex March 10th, April 25,26, and may 3rd. Today is May 4th and I started having cramps this morning with some brown and now pinkish/red discharge not enough to fill a tampon or pad its mostly just when I wipe is this my period being late or could it be implantation. I took a pregnancy test urine today and it was negative?

The time for you to have become pregnant would have been April 7, 8, 9. It is unlikely (but not unheard of) you would have gotten pregnant on the dates you listed that you had sex.