I get shortness of breath, as if can't breath in enough air, so its easier to breath through mouth. some times chest tightness & cough what could it be?

Many possibilities: See a lung doctor for further evaluation. Asthma comes to mind as most common in your age group, but other conditions need to be considered as well.

Worth checking out: It's hard to know, but you could be having symptoms of asthma or another lung disorder. You should visit a physician for an evaluation and exam.

Breathlessness: Could be asthma/ allergic rhinitis/ anxiety just to name a few. Anything that causes breathlessness/chest discomfort is worth mentioning to your doctor and being evaluated.

Get checked out ASAP: One of the most common errors patients and doctors make is assuming that because someone is under forty, they cannot have a serious cardiac or pulmonary condition. That is simply not true. You could be having an anginal equivalent - in other words your shortness of breath could mean your heartis notable to habndle thestrain being put on it. It sould also be pulmonary in origin. See your docto.