My period was due 3 days later, but it is bright red blood and has some clots, and isn't too heavy, i had sex 5 days ago, is it implantation bleeding?

Implantation bleed: Implantation bleeding is much more common on the internet than in real life. It occurs rarely and exclusively in someone who is pregnant. The only way to know if someone had implantation bleeding or just irregular menstrual bleeding is to wait and see if you are pregnant. If your test is positive then this was implantation bleeding. If it is negative then it is just irregular menstrual bleeding.

Implantion: usually doesn't cause bleeding. When bleeding does occur the amount is tiny.