I have red bumps all over my butt. they don't itch or hurt. i've cleaned my bed sheets lots of times but they still appear.

That is strange.: If the rash appears only on one part of the body, the cause is usually something that affects that part of the body, such as contact dermatitis. But dermatitis usually itches badly. A non-itchy rash can be something serious, a manifestation of systemic disorder or internal organ disease. Try using Hydrocortisone 1% cream, but if that doesn't do it, you should see a doctor for some tests.