Never had morning erection since puberty

Sir since puberty I have never experienced waking up in the morning with an erection. I used to do masturbation 5-6 times a week. Last year I comes to know that men's usually wakes up with an erection which I never had. I created extreme anxiety over that may be because I am taking it as lack or deficient in manhood. I ask many doctors they said it's normal if u r getting erection otherwise. But on Internet it's written that lack of morning wood may be due to testosterone or Nitric oxide deficiency, or their is issue in blood flow or may be I am getting it during  REM sleep but by the time I wakes up its goes down. I want to know some solid reasons of not getting morning erection in my last 12 yr normal for many boys as doctors earlier don't gave me any reason except that it's a biological think even medical science don't know? My testosterone present level 297 goes down due to constant anxiety from last one year. Sir please clarify the entire issue with full medical science backup.