Any advice or suggestions?

I am a 53 year old single man that does not drink or smoke. I work out 3-4 times a week and am in decent to good health although I have been diagnosed with traumatic brain injury because of an accident. I have sex typically 5+ times a year (more if with the same girl) but I usually take a Viagra pill out with me whenever I go out just in case. I fear/think my erection “strength” is psychological although everything I have read says it is almost completely physical and caused by blood circulation to the thingy. Also, my thingy stays good and erect for about 15 minutes after penetration and if I don’t cum during that time, I have to take a break and try again in about 30 minutes to an hour later. I avoid taking the Viagra as long as I can because I have noticed when I take it, it effects my vision or I get a headache so I’ve tried to stay with a lower dose of 25mG but have gone as high as 50. I am hesitant and am embarrassed in pursuing a longer relationship with a girl that I have had already sex with because of fear of my “lack of” erection. PS It has also happened with girls during the “first” intercourse. I have tried PEMF pads with no effects and am currently trying a “shockwave” device to improve circulation on the thingy. Any advice or suggestions?