I don't think you have brain damage at all with a fine mri and ct scan. and it doesn't sound like you have post concussive syndrome unless one of those rapid head movements was really really intense, what are they specifically? Sure some of those symptoms fall under PCS but they fall under many other headache and upper neck injury symptoms as well, and the issues you've had would probably have been more persistent than what it sounds like you described.
Also, if that medicine helped before, why not try it again? They use those "anti-depressant" meds sometimes with the intention of releasing pinched nerves and synapses in your brain and head, rather than for depression. That's why they prescribed it, so it almost sounds like you do have tension headaches. And even if you did have pcs (which i doubt), time would heal it, and at 21 youth is on your side.

P.S. I think you're over-thinking things too much, relax a bit