Why am i always dizzy?

I am dizzy all the time. Whenever i stand up, sit up from laying down, or hold my breath for any amount of time, i nearly faint. I’ve asthma so i need to hold my breath to use my inhaler and that makes me black out sometimes. If i have caffeine or sugar my dizziness gets much worse. I drink a lot of water and eat fairly healthy. I went to the doctor and she said my blood pressure is fine. Often, i begin sweating and itching when i get really dizzy. Does anyone know what could cause this?

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Answer:
It could be lots of things, like not eating enough sugar, or eating too much sugar. It could also be diabetes, if you get itchy hands and feet. Don't worry, but get it checked by the doctor to be on the safe side. Hope this helps.