Bleeding after sex

So I'm 18 I had sex yesterday and we didn't go insanely rough or anything and when we finished I noticed that I was bleeding like crazy! My period ended exactly a week to the day before that so I shouldn't have any reason to bleed but now today I'm kind of spotting and am having some insane cramps in my abdomen. This is the second time this has happened in the last month. Any tips, suggestions, advice, opinions, or thoughts of what may be going on is GREATLY appreciated. Thanks.  😌