What causes tiny clustered blisters on the buttocks? they are not itchy or painful, they have fluid inside.

Possible Herpes: If it occurs at the same general spot on the buttocks , Herpes is likely. If it occurs at different areas at different times it is likely " Folliculits" , ie inflammation of the hair follicles on the buttocks

Blister: This needs to be seen to be certain. It seems like herpes type 2 or shingles

Agree with Dr, M: It is prudent to see a doctor to ascertain if it is herpes or folliculitis as the treatments are different. Have a healthy diet, exercise 30 minutes/day, drink plenty of water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV and Covid vaccines. Wish you good health!