Your trainer is misunderstanding the value of Creatine. It reduces the injury if in the blood and tissues before the concussion. It's value when used after the concussion is not shown to make a difference in recovery. It does not appear to have a negative value during recovery. But, muscle building effort during recovery is not recommended as it requires the 'tear down and rebuild stronger' effort. This can flood the blood with the toxins from muscle breakdown. Not good during recovery. Just a note as it does not appear you are exercising to this point.

Glad to hear you have good objective support from your husband. His observations are valuable. You would do well to focus on small improvements. If you can maintain 75% for a couple weeks without causing a setback, chances are you will get to 80% for the next 2 weeks. 2 weeks is a common period of seeing improvements.

My best to you.