I have welps on my buttocks and it itches... I have scratched so much it bleeds what could be causing it

Do you mean welts or whelps? Welts are red bumps, ridges or swellings of unbroken skin raised by a stinging blow or by an allergic reaction to foods, drugs or insect bites. Whelp means give birth to puppies. I'm guessing you mean welts.

If they itch so much that you scratch until they bleed, it's time to see a doctor.

Yes I mean welts.. sorry