You were trying to fix something that was not broken - never a good idea. I do not think that it is the herb itself that's causing the problem. Rather you have switched your awareness during intercourse away from enjoyment to wondering how things are going. Discontinue the Horny Goat stuff, concentrate on your point of no return, at that stage discontinue all stimulation and let things settle down. You can practise this during masturbation. I think you will be fine with a bit of practise and chilling out. Good luck.
Thank you very much Andrew. I stopped and seems to get rid of it.