A right hip flexor strain is what has been waking me up in pain, it's what has made me limp and what has interfered in my routine at the gym. It is what I thought was a Baker's cyst - (diagnosing from Internet sites is unsafe). So the Physical Therapist showed me an exercise that helps the hip flexor, which I'm supposed to do ten times a day.
Getting fit can be complicated. It is simple if you are young and healthy - just eat right, move more, get enough sleep. Geriatric fitness is a different animal. My yoga teacher thought I should take "chair yoga". Thanks but no thanks. I'll get the hip flexor fixed and come back later.
It might take more effort to get to a reasonably stable routine, but hope gleams brightly, fueled by success at weight loss and at weight exercises. Small improvements add up. Just keep going.