Breathing issues and heart palpitations ?

Before I start, yes I’m already seeing a doctor but with no results:

I’m a 20 year old girl with a BMI of 27.5, if that helps. So I’ve been having heart palpitations for a bit now. Normally they start at night when I’m sleeping because I stop breathing. So I’m being tested for sleep apnea. But on top of that, I haven’t been able to breathe well AT ALL for the entire day, which has been going on for months. When I breathe I get a weird pressure-like feeling in my “throat” and near the heart on the left chest. I’ve had to start mouth breathing almost 24/7 because of that, and even then I can barely breathe. I constantly sound like I just ran with how heavy I have to breathe. I got a new inhaler that’s stronger but it doesn’t do much. Does anyone have any idea what’s going on?

I try to exercise and I just get bad heart palpitations and I’m too scared to keep trying because I’m unsure what’s happening. 

I’ve also cut out any coffee which seems to help more but not all the way