How to rule out the cause for erectile dysfunction?

Hi doctor,

I am a 46 year old male. My weight is 75 kg and height is 6 feet. I do not have diabetes and BP. I have asthma which is under control. I am facing problems in getting erections. It is getting worse with time. I tried some treatments for depression and practiced relaxation techniques with no success. My erectile dysfunction problem is there during each sexual activity. The problem started some five years ago. I used to take Viagra 50 mg. The result was good initially but the hardness lasts only for 30 minutes maximum. I could not bear the side effects like headache and face swelling. Even that tablet is not working for me recently. My problem reached to unmanageable levels recently. I get early morning erections. I would like to be treated for this. I would like to know what tests to be done for identifying hormonal or any other deficiency. I will provide any other information as required. Thank you.