Breathing is really hard for me!?

I'm 13 years old. I'm a young girl, who is 5'8 and weighs about 160-170... That's not overweight? I play Hockey, and Softball. I don't know but whatever I do, I can never breath. Running, walking, even sittign down doing nothing. I can't breath doing that. It scares me, because when I am sleeping, I cannot breath. I have an inhaler ( it's not mine. my moms boyfriend let me use his ) and sometimes it doesn't work.. Is this just asthma, or is it something more worse?