confused and scared

i’m almost 18 and a few months ago had sex with my boyfriend for the first time. the first time we had sex i was late for my period by a month and thought i was pregnant but started but i was still late by a month. even took pregnancy test and came back negative, now i’m like a week late? maybe more, and i’m scared i may be pregnant again, it’s been 3 months since i was late for a month and i’m not sure if it can happen again, could i just be stressing to much or should i worry?