Hi, so your DHEA levels should be OK as well, but then DHEA does 3 things if lifes your testosterone, boosts your libido and energy levels, now Tribulus will do all the same things and would be best for you, its a herb and DHEA is a hormon, as DHEA is for us old guys.
But then it could be nitric oxide levels down, Garlic and Cayenne will help lift it back up, OK so chop up a whole head of garlic fine and mix with olive oil and take 3 small spoonfuls 3 times a day, the Cayenne mix with tomato paste and thin with olive oil, and again take 3 small spoonfuls 3 times a day and alternate these and just take for 5 days and rotate, see how you go.
Any luck since you posted this????
Where you taking any workout supplements???
Hope all is well, hang in there buddy.