Why am I absolutely exhausted? I'm back from my holidays now 2 weeks and have zero energy.?

could it have been the sun draining me? I felt recked when I was over there aswell. Sitting at my desk in work now and my eyes are closing. I have recently had a different opinion of exercise after my 40min sessions completely have me recked after it too. im 24 male. have a really good diet and drink loads of water. dont know wats wrong. dont like it anyway! I wonder could it be work? this past while i have been getting up at 6.45 to start work at 8 to finish at 4. Any suggestions?