how many times a week do you shoot. i'm getting some friends of mine into archery and they are a little older so we starte them low# and i told them to pull their bow back and hold it for about 10 seconds 4 times almost every day to build up their "bow" muscles.

It could be cause you are shooting to much. i know if i try to stretch my shooting sessions out i can feel my arm getting weaker as I go on. dont push your self to much.

just some options.not for sure though.