I feel sick and dull all the time

Hello, im a fairly young teenage girl and I feel like I'm going to faint/collapse all the time. And this is interfering with my studying. I can't study well nearly as much as I used to be able to. I don't have a fever or anything- and I've never been diagnosed with any sickness in the past. I used to be athletic and active but these days I've quit gymnastics and rarely go out and be active. And I really can't right now because I feel like throwing up and fainting not long after I start. This has been going on for majority of the year, sometimes it's not as bad and I just feel a little bit dull but other times I can barely walk up the stairs without feeling like Im going to faint and walking to the bathroom down the hall sounds like hell.

A lot of people say that it's just part of being a teenager and "growing up" with the hormones interfering etc. but it's becoming a little too much for me. I'm not depressed nor have anxiety disorder (I think). These days I have almost no motivation to do anything like my favorite hobbies (Playing the cello and drawing). The only time I really am happy with is when I'm laying in bed sleeping or chatting with my friends on skype on my phone while in bed also. My parents just see me as being lazy and when I try to talk to them about it they fake pity and do nothing about it in the end.

Sorry for the complaining... Now for the actual symptoms I feel:
My head feels clouded and murky all the time and I can't necessarily think clearly all the time- I'm much slower with doing my homework now.
When I exercise (or sometimes even just walking up the stairs) at all my head feels kind of like something is squeezing my head at the sides.
I constantly feel like I'm lacking air and I need to take deeper breaths. There's also that sick feeling in my chest and down to stomach area kind of like when you drink too much water and you don't want to move at all. The biggest symptom I think though is feeling dizzy/light headed. Even simple yoga makes my eyesight go blank in front of me kind of like when you're laying in bed but you suddenly get up and feel dizzy. That's normal sure, but I'm feeling this constantly.
Is there something I can do about this? Change my diet? Exercise somehow? Also, I am of healthy weight and fairly fit.