I started having headaches in the morning and sleeping for 12 hours a day?

Recently, I started to sleep a lot, around 11-12 hours a night... and always after I wake up, I have a headache that last for around two hours. Everytime I wake up I have a headache, and if I get up earlier, my head will still hurt and I’ll eventually fall back to sleep during the day. What’s happening? My headaches are mild, but they and a fact that I don’t feel rested after 12 hours of sleep is irritating me...