this was weird for me

so I had my last period on the 18th of July. they usually last 5-7 days, so a normal, typical period. I did have sex during my fertile window. well on the 16th I thought I was out bc I thought I started my period but the thing is, it lasted literally 2 days! like the first day was kinda heavy and the 2nd day was almost non-existent. I've never had that to happen before. has anybody else experienced this? what could've caused it to be like that? could i still be pregnant or is that just wishful thinking? thanks in advance.