I Am 52 And Had A Stent Replaced In My

I am 52 and had a stent replaced in my heart 2 months ago. I am doing cardio rehab but find that half way through the day I have no energy and must take a nap. How long does it take for the body to recover from having a stent placed in the heart? I also had CABG X4 in 2001 so the new stent was used to replace an previous stent that had collapsed.