Should I be concerned that my Caff keeps giving out on me?

This seems like a pretty common side effect from your operation. Your doctor told you it would take a year to fully recover in your lower leg. I'm pretty sure that this is just one of those roadblocks one faces after having a surgery like yours. I would definitely let the doctor know, but I wouldn't be too worried about it. The doctor might be able to change your exercise routine or give you a muscle relaxing medication or treatment that could prevent the muscle from giving out on you.