Breathing problems, please help?

Hi, I'm a 21 year old male. I've had trouble breathing since 2009, when my last ex broke up with me. It seems to worsen under stress and the more relaxed I am, the easier to breathe it is. Simply breathing through my nose doesn't seem to be enough and I have to use my mouth for both inhaling and exhaling. It feels like my lungs close up before I get enough air to them. Sometimes I seem to automatically take really fast breaths and it eventually starts hurting. Any advice on how I can make this stop, or at least soothe it? I have an inhaler that my dad uses (he suggested I use it), and it does help a little but not much.