Been shooting the same Shrew for over 5 years and just in the last couple of weeks the string has been slapping my arm. Although just slightly, bare arm, it does hit the sleeeve if wearing anything long sleeved. What might cause this? It's just one of things I liked about this bow. I never worried about the string slap. Any ideas?

Has the brace height changed?

Sounds like you have shifted your elbow rotation to me. Another thing that helps with that is slightly opening your stance as you address the target.... if all else fails try canting your bow to about 1 o-clock.