I am getting thirsty often even consuming water often, more than 5 liters per day. Still I feel thirsty when I did not consuming water. Also I feel dry in my head always. I think it was the outcome of over heat in my body but I want to know the correct reason for this.
It might be diabetes
As others have said, it might be diabetes, or it might be something else. You may need some lab tests done.
Untreated diabetes can cause worse problems
If you do have diabetes, and you don't treat it properly, it can cause worse problems. Therefore, you should phone a doctor today and book an appointment.
If you can't afford to see a doctor
If you can't afford to see a doctor, seek charity care.
Some diabetes treatments cost more; some cost less. The expensive ones may be the best and most convenient. But, if you can't afford them, ask the doctor for cheaper treatments.