[Llamamoe]

Most people with traumatic brain injury suffer from pituitary dysfunction[1], most commonly growth hormone deficiency, which causes severe fatigue and cognitive difficulties. You should make sure you're checked for that.

Also, don't let specialists stop at brain scans if they're alright, make sure you get someone to take a look at your spine and ceberal arteries.

If those yield nothing, get checked for Craniocervical Instability, a condition in which your spinal disk joints are unstable which can result in nerve or artery compression. This often causes fatigue, headaches, hearing ringing or your heartbeat

You could also try neurotrophic substances, which promote both neuroplasticity and repair from injury- in most countries, cerebrolysin is available as medication. Failing that, you can get 7,8-DHF and its 4'DMA-7,8-DHF cousin from nootropic vendors. Both are highly selective and thus unlikely to have undesirable effects.

I hope any of this helps.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6000755/?report...