I ignored my doctor's advice for years about my low testosterone (in my case, a side effect of my HIV infection and, a little later, HIV-related wasting). Like you, I still had great sex drive and no problems with performance. Then I noticed a lump under one of my nipples and asked my doctor what was going on. It turns out, my testosterone was so low that my breasts started to develop. My doctor started me on testosterone injections, and later switched me to Androgel, a gel product applied to the body. I really didn't like the gel, and hated that my good-size balls shrunk. But, on the other hand, the added testosterone coupled with a good weight-lifting regime, added pounds back onto my frame which I needed. And I think my mood was also better, although I would never have been described as depressed beforehand.
I later switched to an oral prescription for clomiphene, which is labeled to increase fertility in women, but is used off-label in men to re-start their body's natural production of testosterone, just like what happens when we went through puberty. It was quite successful, my natural-production of testosterone kicked back up, my balls grew back to normal size (which caused a little discomfort which was the only side effect) and I found out that a short-treatment period with this cheap, oral medication was a total cure and I was fine without using anything any more. It has now been over 6 years off clomiphene and my testosterone levels remain happily in the normal level.
Ask your doctor about this approach and if he/she has any experience with prescribing it. You can check online for some peer-reviewed medical research papers on its use.