Pregnant or What?

Last month (March) my period came on the 8th it was lighter than normal. It went off on the 10th. Some really light pink blood came back on the 15th was only there when I wiped and lasted until the 17th. I had a pap smear done and a pregnancy test.. No pregnancy.. the test was negative, but I was diagnosed with Chlamydia and HPV. I took the pills for Chlamydia the first week of April on Friday. Im waiting on appointment for further testing for the HPV. Today is 4/15 I was supposed to receive my period on the 11th my period is 5 days late. Is it the Medicine, Stress, The STDs, or pregnancy? When should I expect my period? Help me?