Welcome to HCM
If you have had a blister
which was not painful for many days then it could be an STD
most common being syphillis. If you do not have any history of unprotected sex then it could just be a boil or furuncle
which is caused by staphylococcus
bacteria. But this blister is usually very painful and is filled with pus always. Itchy papules on buttock are common due to moist conditions provided by increased sweat and tight clothes, for both bacteria and fungi to grow. Hence personal hygiene is of utmost importance in such regions. If the bumps have been there for more than a couple of months, then could be of fungal origin. I suggest a visit to a dermatologist
for treatment for both blister on inner thigh and on buttocks.