There are good supplements to replenish your vigor and vitality which will work synergically with a good antioxidant packed with micronutrients which will boss ur immunity and make you more resistant to heavy duty activity. There are good treatment options available today for your issues but you need to take an online consultation from a certified competent experienced clinical sexologist at the earliest to regain that old vigor.

From your description, it appears that you have simply not allowed yourself to sexually desire your girlfriend before initiating sexual activity. You do not need any medication for your condition. Simply cut down your sexual activity, and it will be as good as it was when you started. Good luck.