Blisters forming on the back of my thighs/butt

Question

Recently i started a new job running around a lot (havent worked in a few months)First time occurrence of blisters (clear fluid, small to the size of a nickle, thin skinned/ruptures easily) on the back of my thighs and under my butt cheek, also a couple on the top of my front thighs. They don't itch, but are painful once ruptured, and the rubbing of my pants at work doesn't help. There's probably about 25 on one thigh and 15 on the other. Are they just friction blisters? I've never had this issue before, but I'm thinking it's because of my pants (only have 1 pair atm for work, and they're new).