Testosterone levels in late 20's early 30's

Hi Marc, long time viewer, love your work! This is my first time sending in a question. I am 29, I've always lived an active lifestyle, track and basketball in high school, I was in the military and I've always worked physically demanding jobs. The military is what really started my drive to work out though. I've always been small, I am currently 160 at 5'9" and around 10-12% bf. My question is, I feel, especially the last few years, that my T levels are lower than normal. Who should I see for this? Is this something my normal doctor can test and or treat? Or do I need to go to an endo or some sort of specialist? Thanks for your time, and a big thank you from the veteran community for all the work you do for us!

                               Doug