Help! Im always tired!

Im 5 months postpartum, i dont breastfeed and baby girl sleeps all throughout the night. I can get 8-9 hours of sleep and still be extremely tired. I take naps when my baby does. Today i got 7.5 hours of sleep. Baby girl took a nap and we slept 2.5 hours! (I never do that, i try to keep her naps short). I feel like i cant function. I feel frustrated that everyday i feel so sluggish and have no energy to do anything. As soon as i get up to do something, i feel like i have to no energy and just want to go to sleep. I feel trapped. I literally cant do anything. Also, most of the time when i try to take a nap, i cant fall asleep, i just lay there feeling sluggish and lazy. Ive also been getting headaches. The type of headache you get when you havent slept or eaten, but ive done enough of both of those things!