What to do if i suffered a major concussion. could it mess with my personality?

Sure can: Concussion leads to changes in brain function. It is not unusual to see change in behavior (loss of inhibition, impulsiveness, moodiness etc) after concussion. This should clear up unless you get hit again (repetitive trauma may cause structural brain damage and permanent brain dysfunction as seen with boxing champion muhammah ali).

Yes: Personality ay be affected for as long as several weeks to months.