I am 20 years old and i have done a lot of work in the last few days which is causing a lot of pain in my head. please suggest me a good medicine?

One connection between overworking and headache is lack of sleep and rest (sleep) may be all you need at this point. Otherwise headaches have to be evaluated, specifically if prolonged and your best reference remains your doc. It is somewhat atypical to have headaches from physical work, most commonly due to stress (mental mostly).

It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor and discuss if you may be depressed. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated. Drink more water. Wish you good health!