Alex
Low sex drive is also a symptom of low testosterone. See my other posts about neuro-endocrine disfunction (hormone imbalance) caused by TBI. Its a common issue. Per the article below it may clear up on its own and it may not. Get checked wither way. In my other posts I mention the minimum you need to check although this article covers everything.
Head Cases: Pituitary Incidents Arising from Traumatic Brain Injury - Endocrine News
I would also suggest you get your neck checked as everyone state on this forum.