Using HRV to track fatigue for CFS

Recently my doctor advised me that I "likely" have chronic fatigue syndrome. He advised aerobic exercise in small amounts and gradually build it up until I feel better.

If my doctor is truly saying I have CFS (Also known has myalgic encephalomyelitis) then post exertional malaise is a major symptom and can be detrimental to a ME/CFS sufferers health.

So this week I've been using Welltory to track how my body is doing during a regular week. No additional exercise, just my job and crashing at home.

I've had people tell me that HRV is too irregular to be a good tracking system for this. Though I've seen that the app has already suggested that I could be fatigued and offered me the quizzes related to fatigue. It even had insight reports regarding fatigue made from stats taken from last summer/fall that I just noticed last night.

Anyone have any input on if HRV is good enough for my purpose? I don't have anything else. Also any advice or tips on how to continue for the rest of my tracking week? What parts of my reports should I be showing my doctor? Is there a big daily report/summary I can download as a pdf and print?

Thanks!