Here's my story...
I found out I had low T when the wife and I were trying to get pregnant. At the time, I was 47 or 48 and we'd been trying for six months without any success. She went to her OB/GYN and the first thing she said was that I needed to get my contribution to the project tested.
Oddly, I had a normal sperm count, but they weren't swimming; my motility was less than 2%. My wife's gynecologist referred me to a urologist that basically said that I had low T (total T in the low 100s if memory serves) and there was nothing we could do; we just needed to go with IVF.
I thought this was weird because we'd tried several years before and she got pregnant the first month she quit taking the pill. Unfortunately, we lost that one relatively late followed by several deaths in my family and my wife's. It was several years before got over all the trauma and started trying again with no success.
So, I went to my internist and complained that I wanted to understand what's wrong. He said that was not his specialty, but he would refer me to an endo he referred to as "the guru". Well, the guru was popular because it took me months to get an appointment, but I finally got to see him.
He had me go for an MRI of my head, which found that I have Empty Sella Syndrome. As I understand it, there's a membrane that separates the pituitary gland from the intracranial fluid around the brain. If that membrane develops a leak, the fluid gets in under pressure and squishes the pituitary gland up against the inside of the saddle-shaped cavity where it sits. In an MRI or other image, the sella appears to be empty because it's filled with fluid. He told me that the pituitary gland is still there, it's just squashed. They don't have any explanation of why it developed; they did further checks and found I don't have a tumor or anything.
When this happens, the pituitary gland keeps functioning in general. My growth hormone, thyroid levels, and such are normal. But, apparently there are two hormones the pituitary releases that regulate the testes - follicle stimulating hormone and luteinizing hormone. I don't recall which, but the one that was signaling the testes to make sperm was okay but the one signaling them to make T was not. According to my endo, this is not uncommon with ESS.
For the sperm to mature and become motile, they require endogenous testosterone. That's why my sperm were immature and not swimming. Externally applied T won't work for this purpose and will shut down the whole works.
So, he started me on HCG to increase production of T. Over the course of a year I got my T back up in the 300 range and the motility increased to about 25%. I think if we'd had more time we could have gotten it up to 40% to 50%, which apparently greatly increases the chance of conception. But, my wife was approaching 39 and we wanted to go before she hit 40 to avoid genetic complications. So, we ended up going with IVF and have a wonderful 5-yo son today.
As soon as she got pregnant, I went on T replacement in the form of Axiron under each armpit. That actually resulted in excessively high T for me and after a year or two I developed hypercythemia and had to cut back. Today, four years later, I am on Androgel 1.62% for two pumps and my total T is around 675. I have zero sperm count, which is fine with me as my wife and I are done with the baby thing.
I still would like to know why I developed ESS; I'm pretty sure the low T thing wasn't a problem in my early 40s. The only thing I wonder about is that I did powerlifting as a hobby for a number of years in through my early 40s. Although it never happened to me, some of the other guys I trained with would actually get burst blood vessels in their eyes from straining so hard. I have speculated that perhaps I had some defect in the membrane, but that it took my powerlifting years to bring it out. I asked the endo about this, but he didn't seem to think it was likely, but he has no explanation for why I've got it.
So, there's my story - I hope you can figure out what's going on with your T. I've only had one endocrinologist, but he was the one who figured it all out. We considered naming our son after him, but he has a funny name...