possibly being pregnant???!!!

i got my period on the 1st of july and ended on the 6th. i got it for the normal amount of time but this time round it was pretty light. i had sex with my boyfriend on the sunday and we were using condoms so we did have protection! but didn't for the first round but his 100% he didn't cum in me cause he pulled out. this tuesday that went past i got my period again and it was bright red and all day i had it but the next day (wednesday) was a bit lighter and today i have brown discharge.

i read up about it and a few things told me it may be caused from stress, becoming sexually active, first signs of pregnancy or having my period short this month and having sex could have made in come back.

i'm abit scared on what this means. can someone tell me?? this has never happened to me before:((