Hello! Today I Am Supposed To Get My Period Since

Hello! Today I am supposed to get my period since I am on a 31 day cycle and my last period started on July 24th. I had unprotected sex on the 2nd of this month (only precum no real substantial semen, he also peed in between). I believe I began ovulating on the 8th. Ok the 15th I experience a horrible stomach infection that lasted the better part of four days. I took a pregnancy test on the 20th, 4 days before my period was due using the first response brand. I tested negative for pregnancy. On the 22nd, I had protected sex which became painful deep inside. Today and yesterday I have had very slight lower abdominal cramping and a mild burning sensation in my Vulva. I still have not gotten my period and I am very concerned that this means something more. Do I have a yeast infection that is delaying my period? Am I pregnant? Is all the stress delaying it? FYI I have always had very regular periods and never missed a month.