The headaches and the weight lifting lead me in to directions.
1. TOS - Thoracic OUtlet Syndrome sometimes connected to weightlifting and the headaches can also be connected. Do you have any numbness or tingling in the hands?
We have a TOS board where you can ask more questions. Here is the link for the TOS board.
http://neurotalk.psychcentral.com/forum24.html
2. Possible neck flexion issue - meaning cervical neck may have gotten unstable from the injory. Often called a subluxation or retrolithesis. MRI might not show but EMG and flexion extension x-rays might help pinpoint.
3. Cervical disc issue
MIght be worth seeing an ortho or a neuro
Keep us posted.
Shelley