Once in a while, I have this weird feeling in my chest that I cannot get enough air. I breathes fine, but it seems like my lungs are not capable of getting the oxygen. I feel very weak and dizzy because of it. Even though it only happens once in a while, for a sort time, it happens.

I would breath in and feel as if I had not, just a little bit better. I even have the feeling of being suffocated, while I'm not.

It doesn't just happens in closed places, sometimes it happens outside too. So I don't think it's the air that's the problem.

I even gone to the doctor, he said that it's fine (he didn't do any tests like blood tests... ) and that I will grow out of it.

I've read on the Internet, it said that there is a symptom where your blood doesn't have enough hemoglobin? What if I have that? And how do I tell? Thank you in advance.

I think you should see a another doctor and get a second opinion.

Asthma, anxiety... those come to mind.

Go see an Allergist. Could be the result of allergies/asthma.