I have a sore on the top of my butt, it's raised and is a cluster of white bumps all bunched together and is surrounded by redness. it itches and it's sore. i laid in tanning bed and when i got out,it was bigger. what is it please??

Likely herpes, either herpes simplex virus if you have had past genital or anal area herpes (maybe without prior symptoms); or herpes zoster (shingles). Either can be triggered or made worse by UV light. See a doctor ASAP, diagnosis, testing, and possible treatment. The sooner the better for most accurate diagnosis and most effective treatment. Don't pop bumps or otherwise or otherwise mess w/ it.