I sleep for long periods every night over 12 hours, i'm always tired. is there something wrong or is it just over sleeping?

Many possibilities: At 24yo, if you are tired enough to sleep for 12 hours a day, you probably need to see your fp to sort out a few things. Check for anemia, low thyroid, or other metabolic problems like diabetes. If those are clear, an exam & ekg may show some heart abnormality. I doubt you have sleep apnea, but you could do a home sleep test to make sure you are getting adequate rest during sleep. Get checked out!

Sleep quality: It sounds as if your quality of sleep is inadequate. You need adequate time in various levels of sleep to feel physically and mentally refreshed. You may need a sleep study to more fully diagnose your sleep patterns. Ask your doctor to refer you for a polysomnogram/sleep study.