Don't know if i had unprotected sex

Hello i had sex 3 months ago, i had to much to drink and cant remember if we used a condom. i havent spokn to the boy so i cant ask him if he did. i havnt missed a period they have been pretty normal or i havnt put on wight but i keep thinking im pregnant and its really gettin me down. i have taken a pregnancy test and it can back negative, but it was a cheap test.
i havnt experienced but do feel bloated, im really worried and dont know what to do
please help
thankyou.