am i pregnant or stressed?

hello! my period is 10 days late and im not sure why :/ i just came back from med school and i was super stressed towards the end for finals and then i went on a trip to spain for 10 days where i was supposed to get my period but didnt. ive taken 2 pregnancy tests in the past week and both are negative. i dont feel anything strange but also dont feel my period coming. last semester i came back home after finals and my period was 7 days late, most likely due to stress. my bf did finish in me once during the second day of my last period but that has never resulted in pregnancy. so basically is it stress, travel to a different time zone, or pregnancy? im slightly concerned. im usually pretty regular around the 32 day mark.