Why do I drink lots of Energy drinks and am still tired?

I'm 23, healthy, well mostly, I have a lot of pain issues that have me on Tramadol to help, I sleep like a baby, at least 7-9 hours a night, I have a great job that doesn't stress me out, two kids that yes are stressors but not overly. EVERYDAY I drink 4 or more red bull and a 5 hr energy shot and nothing... I can yawn right though my day.. I do have low blood pressure, usually 90s and that's really it... I know some people that drink 1 red bull and have the shakes from it... I'm just wondering if that's normal or if it's something that I should get checked out. I did tell my doctor because my co-workers were concerned with how much I drink but he said it was fine and shrugged it off, but I guess i'm not convinced.. I've had a LOT of blood work done recently and there's really been nothing found that anyone is concerned with... low Vit D, that's about it and i'm on Vit d supplements. Any thoughts or suggestions??