Hi, you may be probably having Circadian rhythm disorders. Due to long term sleep deprivation in night time or delay in sleep will lead to excessive day time sleep or sleepiness, which happens due to change in normal sleep-wake cycle. This is termed as hypersomnia of central origin. If stress is present, you need to go for relaxation exercises.
You need to undergo tests like Polysomnography, Multiple Sleep Latency Test and CSF levels of Orexin/Hypocretin which help to substantiate the diagnosis. You also need to get evaluated for depression which includes loss of pleasure, social withdrawal, tiredness etc. Get your thyroid profile too.
Drugs like Modafinil, Methylphenidate and Amphetamines against prescription can help to increase the alertness during the day and they are esp. useful in excessive daytime sleepiness.
I suggest you to consult physician/sleep specialist for further evaluation. Take care and regards.
There are a number of things that can cause this. Do you snore at all? It is possible that you have sleep apnea. If so, it could be that you are tired because you are waking up, even for just a second or so, several times throughout the night and not getting restful sleep. A sleep study can help determine if this is the cause or not.
Depression and stress can also cause this. Has there been anything in your life lately that you might be stressed or depressed about?