Post sex bleeding with clots

I struggle with very irregular periods. Some times they last weeks, others just a few days...etc... I finally stopped bleeding last week, had sex on Saturday night and Sunday afternoon I bled with one large clot.

Today the bleeding has basically stopped. Only using a pantry liner. Any advice or ideas of what the heck? This isn’t the first time I’ve thought my period was over and bled after sex.

Is this my period or something else?