** 1. If you can obtain erection on your own by masturbation, but not with women or cannot sustain it, then the cause is definitely psychogenic (because as you said reasonably fit and healthy) 2. probably anxiety performance or fear in case you fail to satisfy her is the root problem. 3. practice perineal exercise: while urinating, stop the flow of urine, start again, stop and start again 4-5 times. 4. Tentex royal capsule from himalaya, vigor forte Capsule from Ayush, Vigorex tablet from Zandu, you can consult with an Ayurveda Physician regarding the same.