worried about pregnancy?!?

okay so i lost my virginity on may 13th. we used a condom but he didn't pull out and i'm not on the pill or anything. we had sex again the 19th, again used a condom but this time he didn't finish. my period was a day or two late but it did come 3 days ago(today will be day 4). however, it's not like my periods usually are. it's super light to the point that it doesnt even fill a lite tampon. usually my periods are realllyyyy heavy. does it have to do with me losing my virginity and having sex? or could it be something else? could it be implantation bleeding? would implantation last almost 4 days?

ps sorry it's so long it's just a terrible fear of getting pregnant the first time i have sex. also there was no evidence of failure of the condom i'm just worried bc things aren't normal