I feel like I can't breathe?

I am a 20 year old male. For the last 8 days, almost every time I try to breathe, it feels like my lungs aren't getting enough air. I'm getting the oxygen, but my breath never feels deep and "refreshing". It almost feels like something is keeping my lungs from fully expanding. Every so often, I'll get a good, deep, satisfying breath, but they're few and far between. I'm an ex-smoker/chewer who quit a few weeks ago because I'd feel this way the day after having a cigarette, but the feeling came back about 2 weeks after I quit.

I don't really have a cough, and whenever I get phlegm up, it's clear, suggesting that there's no bacterial/viral infection. My throat is slightly dry/sore, but I believe that's from having to breathe through my mouth (I can't get a full breath through my nose). There is also a strange ache/pressure in my lower left ribcage that's exacerbated whenever I manage to get a deep breath. I've never had asthma, and I've tried using an inhaler to no avail. I do frequently suffer from acid reflux, and at first I thought this could be a result of that, but I've been on both Prevacid and Tums for the last few days, yet the shortness of breath persists. I've heard that anxiety can cause shortness of breath, but I've been feeling this constantly, every waking moment for the last week, regardless of my mood/activity level.

I will be visiting the doctor at some point in the week if it does not go away after a week of my medicine regimen, but I figured I'd ask around and see if anyone here could offer suggestions as to what I have.