In 2015 I suffered from brain trauma from a bad motorcycle accident. Since the accident for three months I was fainting once weekly, and it stopped in 2016 in about July. I went through an MRI, blood work, glucose testing, and they never found anything.
In about October of 2016 began to go down hill because my emotions were too severe, and I had no interest in sex (never have, I'm a 20 yo f). Two relationships later, I developed a stutter, combining the ends of sentences to the beginning of sentences, combining words (fantastic and great= grafan???) on the spot, and an utter repulsion to sex. I'll also ask someone a question, like, "Are you working tonight?,' they will respond with no, and I'll say to myself out loud, "No, I'm not." Then immediately think to myself why I said that out loud.
Today, I looked more into it because I noticed I can distinguish a bump on my nail (irrelevant) to be interesting to me, or frustrating that it is there. Same with not being able to distinguish my mother's despair for my grandfather being in the hospital and translate it into my own emotions. In my mind, we didn't know what was going to happen so there was no need to worry or cry.
I am not a medical professional, but I guess your condition can be associated to your traumatic brain injury, it is possible that you have not been fully recovered from it or some of the harms have become permanent.
As far as I know, it is not uncommon for people with a traumatic brain injury to be alexithymic, people with a traumatic brain injury are 6 times more likely to be alexithymic.
I think you can contact your doctors about this to know what actually is going on if you want.