Talk to Sexologist on Low And Soft Erection

My question is before two years my dr prescbie me amitriptyline I took only single dose and i leave so next two days my penis erection become hard and improve in erection.Then for nightfall another doctor prescribe me paroxetine my nightfall was reduced but no improve in erection.Again I myself take amitriptyline for 3-4 days due to headache and dizziness I leave taking amitriptyline but I see improvement in erection and penis become hard on erection.So how to differentiate either it is psychological, low testosterone level or poor blood flow.I am really worried about it