Being productive in between yawns

The hardest thing for me is to decide when to stop and go to bed. It seems trivial when all I can do is yawning. My old me, the one that doesn't seems to need much sleep has been bothered by the new me, the yawner before midnight. I have recruited the help of coffee pods and heavy teas, yawns persists. I tempted my self with great articles and applaudable music, the yawns pushed harder. I seems to stare through the two inches iMac, even though I am actually reading or writing, cleaning images, or selecting few photos out of thousands, given it is not that interesting. But I used to do all this with such easy of unblinking eyes and zero yawn. I am troubled by getting old.