You need to know more than TT.
FT, SHBG, DHEAs, E2, LH, TSH, to start with.
FT3, FT4, TT3, TT4, Prolactin, DHT, Cortisol (preferably saliva), D3(active and storage), would also be nice to know.
If you have secondary hypogonadism (low LH) there are many possible reasons: I'll list a few.
OPIATES, excessive alcohol, starvation(obviously not your case), AAS/PH use or previous use,
Head injury, phytoestrogens (soy, ginseng), pituitary tumor, excessive exercise, STRESS, sleep deprivation,
high E2 levels.