Chest pains

I'm 32 weeks and ever since the third trimester it's been really hard to breathe even when I'm just laying on my side or sitting up I feel tightness and heaviness in my chest. (though I'm breathing pretty normally) I've had doctors appointments and tests and nothing seems to be wrong. My pulse was a little high at my doctors appointment yesterday for no reason. Anyone else feeling like they're just suffocating sometimes :/