i originally started the pill to make my periods normal because they were irregular and its been going well and i've been on the pill for about 1 year now, and over the years i've missed one -3 in a pack everyone im hopeless... haha but i've had unprotected sex many times and never got pregnant, but now im worried.

I started my sugar pills 4 days ago and 2 days ago i had unprotected sex and didn't think much of it because im considered obese i figured its harder to get pregnant anyway but my period normally comes by day 3 and it still hasn't come but i took a pregnancy test yesterday night and it was negative. yesterday i had some reddish period looking stuff and i thought i was started cause that how my periods normally starts but then nothing.. and i had little cramps last night but wasn't like period cramps so now im freaking out that it was implantation bleeding..

could i still be pregnant?? im only 19 and im pretty worried..