9 hours is quantity sleep. How do you know you get quality sleep. Do you wake up naturally roaring to take on the day or do you need an alarm and cup of coffee?
Do you dream? What kind of dreams? Pleasant dreams, stressful dreams...?

A neuro rehab sleep specialist spoke at out TBI support group. She said that sleep is a very common cause of cognitive struggles. She explained the difference between quantity, 9 hours, and quality.

Are you ever tired during the day?

I spent 2 years struggling even though I got 8-9 hours of sleep. When I finally learned how to get quality sleep, everything changed. I can do great with 6-7 hours of quality sleep.

How long do your study sessions last? Do you struggle more when they are longer?

There is a huge difference between memorizing facts and learning problem solving/diagnostic processes. Do you do better with one than the other?

What is your study environment like? Quiet, background noise, music (type), voices, visual stimulation, ???

Neck trauma can cause inflammation that can disrupt blood flow to the brain. The neck does not need to be sore or painful to have inflammation. Mine never did but after I took care of it, thinking improved. I call these injuries Subtle Neck Injuries. They do not image or test as injured but they do cause inflammation.

Do you get headaches at all?

One concussion research program found 80% of concussion symptoms were neck related.

As you say, you are stressed out. You also mentioned having Concussion Anxiety Syndrome and took an SSRI for a time. Research shows that people with a history of anxiety, depression, and struggles with stress have far more struggles with symptoms, especially prolonged symptoms. Resolving stress and anxiety is important.

Does your school have an athletic department with a kinesiology dept that can do a cognitive test, like ImPact or CNS Vital Signs or Brain Minder?

Do you take any supplements? Omega 3 fish oil would be helpful. B vitamins, too. The Vitamins sticky above has a supplement regimen.