over 2 weeks late... please help

hey guys, in the past month my boyfriend and i have had sex using condoms. never has he ever ejaculated inside me, or the condom (he finishes outside of me always), and we check for breakage thoroughly (which the condoms have never broken). there was only one scenario where the tip of his penis went inside of my vagina for about a second (it slipped). today, i am roughly 15 days late, i took a home pregnancy test twice (negative) and i took a pregnancy test at the doctors (negative) as well as a blood test (negative) when i was around 6 days late. is there a chance? i haven’t been eating too much the past month due to a lot stress and i’ve changed my diet from barely drinking water to drinking 2 litres a day. AND NOW i have brown spotting? ew i don’t know if that’s a sign of pregnancy or not but please help, i’m 16 and so worried.