You may be able to try a different form of therapy. It is possible that the concussions have caused slight displacements of either your neck vertebrae or the bony plates in your skull. Even small shifts can cause lasting headache problems. Craniosacral massage therapy can work wonders with this sort of problem. MRI scans look for other types of problems, like larger ligament injuries, brain bleeds, swelling, etc. The clear MRI's are good news! Now go get yourself healing.