Afternoon sleepiness

I usually don't sleep in the afternoon. If i sleep, i wake up with headache and had difficulty sleeping at night.

The best thing to do would be to not sleep in the afternoons. Obviously, if you're so tired that you just can't stay awake, this won't be possible. Have you tried just having a 'power nap'? Set an alarm for 40 minutes after you go to sleep, and try to get up when it goes off. Do you drink enough water, and eat well? These would contribute to you feeling tired a lot. Are you doing anything particularly strenuous to make you feel this tired? Or does it happen regardless of what you're doing? I would recommend seeing a doctor if you're not being extremely active. There are many common causes of tiredness that your GP will be able to help with.