If we compile all the suggestion given in this thread, they look great and I will also add up based on my exp
1. Check your monitor and setting. Are they good enough or they give stress to your eyes. If yes, go for a bigger size monitor
2. Are you taking 5 minute break after every half an hour. Believe me, this is the key
3. Do you undergo regular medical checkup. If not, take Vitamin D deficiency test, deficiency of this will give you muscle plain, tiredness and make u sleepy
4. take out some time to read inspiration story. When you are living in stress, this causes hell hot of issues