Could I have a brain disorder or something from multiple head injuries in martial arts?

A bit. The classic is boxers who generally end up with severe cognitive impairment and early dementia. Football players also are very susceptible. If you have a choice, become a baseball player or a golfer. Martial arts in many ways teaches you to protect your head but some damage is possible.
Possibly. It depends on the extent of your injuries, whether you recovered sufficiently after the injury before returning to full contact etc. There is a lot of research into traumatic brain injury and it's possible association with chronic traumatic encephalopathy. If you think you may have a brain disorder, i recommend seeing a neurologist or better yet a specialist in traumatic brain injuries.