TrumpetScreamer

Well I have been really working on developing my range, power, and endurance in the last few months. I am currently able to hit a High C with alot of power and good tone. I can go higher, but after the high C, I begin to lose the power and strength. One of the problems I have been running into is after I hit a note like High C, or maybe the B before it, and hold it for about 5-10 seconds I get a short headache, normally developing in the back of my head. It goes away after about 5-10 seconds. Keep in mind this is after I have been playing scales for at least 10-15 minutes straight. After about the fourth or fifth headache, they become to painful for me to continue playing. The most annoying thing about it is that it begins to develop before my lips are tired, so I think it is restricting me from building my range.

Is this normal? If so should I just work through it and eventually it will begin to come at later times?

If not does anyone know what I could be doing wrong and how to stop it?

Thanks,

-TrumpetScreamer