So much blood! 😖😥

I came off my period on Tuesday which lasted 11 days, had sex on Wednesday which Glow said was my most fertile day, and since yesterday I have been heavy bleeding again, started brown/black, now it's bright red with clots. Help! I don't know what's happening, it's like my period has come back or something. I'm so so scared, does anyone at all know what could be happening to me?? 😭