At the end of June, I had a UTI. My doctor had prescribed me a 5 day, twice daily, course of cephalexin for this. My LMP was from June 26th - June 30th. My period is ALWAYS regular, on-time and 4-6 days long. I have taken the Plan B pill in the past and it has NEVER altered my menstrual cycle. On July 1st, my partner and I had protected sex, but after he “finished” he decided to keep going with the condom still on. He told me after that, that he noticed the fluid was on the outside of the condom and on the outside of my “area”. I took my first dose of antibiotic the next day as I picked it up July 1st. So on July 2nd, I took both a ceohalexin as well as a Plan B pill. I have taken 3 pregnancy tests now, all of which have told me negative (-). The first was taken on the first day of my missed period, July 23rd. The second was on the 4th day of my missed period, July 26th and the most recent was today, July 31st, 9 days late for my period. I have had mild symptoms including: Intermittent nausea daily for the past two weeks that goes throughout the entire day, left-sided mid to low back pain, irritability, fatigue, headaches almost daily, and light spotting July 8th - July 11th. I had learned in nursing school that some antibiotics may decrease the effectiveness of hormonal birth control, but upon extensive research between cephalexin and plan B, I did not find any evidence of this interaction between the two medications. My partner insists I can’t be pregnant as he has two children already, but I’ve never been pregnant before so I’m unsure. Is pregnancy a possibility at this point? I have had none of my regular PMS symptoms, so I assume my period is still at least a week away, if at all. Thanks!