Hi. So Since Last Wednesday, I Would Have Periodic Episodes

Hi. So since last Wednesday, I would have periodic episodes of lightheadedness and ringing ears when I was walking. It would last no longer than a second. Over the course of a couple of days, it had gotten worse. I'd get the lightheadedness, vertigo, and ringing ears whether I was walking, sitting, or laying down. Monday, I went to my pediatrician to get it checked out. He told me that since I am tall my blood has a hard time getting oxygen to my brain. I've been drinking lots and lots of fluids since then, but nothing is helping. It's getting very worse and I don't know what to do. (I am 16 and don't drive, so i have to ask my parents to take me to the doctor. And since my symptoms are getting way worse, i asked to see my doctor again but they arent doing anything because they said i already saw him I'm and that i am fine. Im not!) Please help!!!