hey mate,, i know we have a bit of a gap in our age but i might have some useful advice,,, first of all my question is have you recently divorced or seperated from someone you really liked. its just that when i split from my first fiancee after 7 years,, when with other women i just wasnt interested in the new person i was with, in the middle of one session i went limp,, it had never happened to me before but i put it to be just out of a relationship, decided to break it off with that person and get out there to find me again,, wait until i really really really starved myself,, i lasted a month with out any, iwas a soldier so i had alot of stress withthat too, so i went out one night and had a few drinks and went to a brothel as you do when your a soldier lol, half way through i went down,, because of the condom i was using was too thick. to this day i cannot use normal condoms,, try the naked ones if you use em,, they are so good, closest to what you can, but at your age im guessing you have probably had a snip so thats probably not the problem... the thing is, when you go limp the first time,, you put down to stress or just abad night,, you get away with it,, then is happens again and you get more embarrassed.. its now at a point that in your mind it is going to happen, no matter what you do, in the back of your mind you are going to expect it so it will happen. stop having sex for 6 weeks,, see what happens,, hard i know but it works,, watch porn and buil you own self esteem up again, because i believe thats what your problem is, its got to you for so long that your embarrased before it happens. build the confidence back.
like i said bigger age gap, but i experienced your prob for quite a while,, in the ed i had to mastabate and slowly get back into it.
Take care, let me know how it goes.
P.s. i hear horny goatwead and similar things make you sick nad drowsy,, but that was only one guy i knew who tried it