I had unprotecteded sex 3 months ago I've been getting my period every month since but this month it's coming 2 weeks early. Should I be worried?

No. You are not pregnant from the previous encounter however you should be worried that you allow unprotected sex and may consider seeing a health care provider to check for sexually transmitted disease.
Probably not. Sperms may be masters of deceptions, but dont have that long staying power! If that encounter was to reult in something, you would've known earlier. In any case, a simple urine pregnancy test can rule out any concern. For the future, try not to have sex without protection, both against pregnancy and STD. Feel good!