This isnt the first time i'm having an irregular period but its the first time i'm having a late one

I had sex last month but he didnt ejaculate...my period usually comes along in the begining of the month but its about 6 days late and i am freaking out...i had unprotected sex two months ago and he came outside me and afterwards i had my period at the expected date so i know its highly improbable that i cud have gotten pregnant before last month...but i've heard of instances when women wud be pregnant and still see their periods so i am seriously paranoid. My period came a few days erly twice about 4 months ago tho so this isnt the first time i'm having an irregular period but its the first time i'm having a late one...i also drastically lost weight within this time frame so cud it just be the stress causing it?? Or cud i actually be pregnant?? I am seriously terrified :(