Why is it that out of nowhere i start to sleep late. if i try to sleep earlier around 11pm my head hurts. ?

Non 24-hour cycle: Do you mean you sleep fine for a while, but then you cannot fall asleep at the usual time anymore? You may have a non-24 hour cycle. Most people have a 25 hour cycle, and readjust by an hour daily. Someone with a longer cycle has a harder time adjusting daily, and eventually cannot adjust - cannot fall asleep on time or wake up on time. Eventually the cycle comes back around with normal sleep.

Sleep cycle: Sounds like you may have a circadian rhythm abnormality. When you have episodes like this, try taking melatonin 5 mg for a week or so.