My Husband And I Are Trying To Conceive. This Is

My husband and I are trying to conceive. This is my first cycle since coming off of birth control. I am also taking amoxicillin for a recent ear infection. Last week I spotted very dark blood for 5 days. This week I was supposed to start my period, but I haven't. I also have had massive itching, swelling, and some redness of my vaginal lips. No discharge. I've taken 2 pregnancy tests-both negative. Could this be a yeast infection, UTI, pregnancy or just a very irregular period?