I Have Been Diagnosed With Chondomalacia Patella, But Got A

I have been diagnosed with chondomalacia patella, but got a hamstring strain during physical therapy for that. Then a reinjury to the hamstring during recovery. It is since mid-October that I reinjured my hamstring and have been very inactive since then. Walking on flat sometimes 15 minutes, some swimming, and the physical therapy exercises, taking off weeks at a time. I was building up activity again and after the stationary bike for 30 minutes, it is very sore again and I have to take time off. Would you advise against a cortisone shot? I am a 68 year old female and fear these long periods of inactivity are very bad for my health but I can't seem to recover.