I get yearly blood tests and I don't know about full panel, but my testosterone range always falls within normal...perhaps it could benefit from a minor boost...but there are other glands and hormones responsible for libido and they may be taxing me. I'm sure the hypothalamus in all it's regulatory glory would be impacting it somewhat. I seem to get libido in phases...can have a couple weeks of constant sex drive where I can't think of anything else, followed by very little interest in it for a couple weeks. It's weird. Prolly aligned to the moon phases lol
A lot of it has to do with tiredness and energy, I know this much. After a heavy gym session of high intensity or even with doms and fatigue the next day, the last thing I feel like doing sometimes is something energetic like having sex. Where this is a big problem is that your partner can take it personally and think it's a problem with them, lack of attraction etc. when it's a problem with you.