I am tired all the time during the day, I exercise, get 6 1/2 hours to 7 of sleep a night, but someone said maybe you should try B-12. I am 56 years old, weight 138 lbs. I didn t know what type of B-12 to look for and if it is determined by your weight. I do take a multivitamin (Complete for over age 50) which does have some B-12 in it, but not knowing if that would be enough. I buy the multivitamin at Walmart.