I find it fascinating that each injury to the head comes with such different symptoms. after 7 years my cognitive difficulties have mostly disappeared. at one time I couldn't even look at a computer and I lost my once formidable typing skills. but they returned. horrifying headaches that made me contemplate suicide for 3 years have largely disappeared although I still get stabbing pains and soreness. what HAS stayed is the REM sleep problems, the waking up in burning pain problems, the bowel problems, the men problems and the standing up and getting dizzy problems and the neck and shoulder muscle soreness. I think this is the cerebellum brain stem and thalamus parts of the brain that were injured in me and not so much the frontal lobe. my autonomic nervous system was shot as I now have dysautonomia. I wonder why some parts healed and other didn't

And it is very possible you have another problem causing your
difficulties. RX drugs like gabapentin and Cymbalta can cause suicidal thoughts. Insulin resistance also is hidden and messes with your blood sugars. Avoiding sugar, and starches, and eating lean protein and veggies, helps with this.

Antidepressants like Cymbalta affect sexual functioning in a major way.

The dizziness upon standing may be due to the Cymbalta, and gabapentin. Also if you do have a peripheral neuropathy this can attack the small nerve fibers in the autonomic system and cause blood pressure problems and GI problems. Diabetics often get Candida infections in the GI tract leading to toxins being released into the body, from them, and also GI upsets.

Have you had your Vit D measured? Low D is implicated in chronic pain, and when fixed, many report lower pain levels as a result. Some of your symptoms sound like peripheral neuropathy and may not be due to your previous head injury.
Neuropathies come from nutrient deficiencies, gluten intolerance, and diabetes. Also exposure to some drugs, like statins, and certain antibiotics damages nerves. Alcohol also can lead to nutrient deficiencies, and nerve problems. So stopping any alcohol if you use it, would be a good idea. Alcohol also interferes with sleeping.