Idk what to do HELPP

kathys

So i just had sex with my friends a month ago. Then one week after we had sex i got my period and the blood is not red is like a brown for 3/4 days. And this month I’m not getting my period yet. Im sacred that i might pregnant which i don’t want it to be happen right now and I’m still 16 years old. So should i buy a test or just wait until i get my period?