I'm tired a lot

I wonder why that is. I've gone to the doctor and had all kinds of blood work and tests done and believe it or not, I'm exceptionally healthy. My liver enzymes are back to normal, cholesterol is good, blood pressure is perfect, and my blood sugar is good. My thyroid is normal. I take all my vitamins and excercise 5-6 days a week. So I'm still not sure why I'm so dang tired all the time. Last night I tossed and turned all night long, until about 4am and then Katie woke me up at 4:45am because she wanted goldfish. Somewhere around here on the page, the bottom I think is my weight loss ticker. I've lost 52 pounds. So, I should be feeling better right? My doctor thinks it's stress. I think if I get any more stressed one day I'll fall asleep and wake up ten years later.