I got bad headache. Can I drink water?
It is hard for me to judge by the terminology that you are writing what you should do. The general rule for breaking a fast on 10 B’teves, Tzom Gedalia, and 17 Tammuz, is that if you feel worse than normal people feel when they fast then you may break the fast. However, if it is just a headache and weakness that most people feel when they are fasting then it isn’t enough to break the fast.
Igros Moshe O:CH 4-114, Piskei Halachos (Bein Hamitzarim) 1-8.