Why can i sing good and sumtimes not?like singing clearly & high, i usually

Question:

Why can i sing good and sumtimes not?like singing clearly & high, i usually can do that but cant at times:' (

i wish i could sing in a high pitched voice and clearly. at times i can do that and sing really amazingly, but sometimes, i just feel like i cant sing at all and my head hurts. i need some tips or reasons why that happens. i take singing classes and try doing the exercises for my voice. but sometimes no matter how hard i try it still hurts or just cant do it cuz my head hurts or my jaw gets tired. i really want to learn how to sing the right way and sing professionly, its my dream !

Best Answer - Chosen by Asker: The first thing I would tell you to do is relax! You sound as if you are trying so hard you're giving yourself headaches. Pushing yourself like that is not good at all for your voice. Don't try to sing too high too soon. Hitting high notes takes a lot of exercise and practice. You wouldn't walk into a gym and try to pick up 500 lb. weights right off, would you? Your vocal chords are muscles too, and they need to be warmed up and strengthened properly before you get too ambitious. That is going to take some time, but if it is your dream as you say, it will be time well spent.