Why Am I Getting Blisters On The Bottom Of My Stump Despite Proper Prosthesis Fit And Gradual Use, And How Can I Prevent Them So I Can Walk And Work?

I am getting blisters on the bottom of my stump after wearing prosthesis
I keep going to tech to check fit assure I am have good fit The tech has checked and double checked to assure I am putting it on correctly and using correct I start out slow 30 min in am then 60 min by day 3 I have blisters I have let blisters heal well before I apply prosthesis and see Prosthesis tech I was a very active person I need to walk again HELP
Many Thanks
PS I am a nurse I need to work