Mysterious shortness of breath, no satisfactory answers

For the past few weeks I've found it absolutely impossible to get enough air. I inhale and feel like I can't breathe deeply enough; it feels like I can't catch my breath and is particularly unbearable at night when I try to sleep. There's also a dry cough associated with it and a feeling of chest pain/numbness that sometimes shoots down my left arm and up to my face. The whole left side of my neck and left shoulder/arm hurt. I've been to the ER several times and they just tell me I have anxiety; they gave me Ambien to help me sleep, but I really don't think that can be a long-term solution.

It all started about 2 months ago when I went to the ER for chest pain that they diagnosed as costochondritis. but the pain got worse, and then my shortness of breath (which I already had) also got worse. I had shortness of breath already which my doctor said was asthma, but ventolin inhaler did absolutely nothing to fix the symptoms. When I went to the ER, they gave me steroids which also did absolutely nothing, except maybe reducing some of the chest pain. They said I had chest wall inflammation and cough-variant asthma. My heart and lungs seem absolutely healthy, I went to a pulmonologist to do a pulmonary function test which came out fine, they just said I had mild asthma. But asthma medications do nothing to reduce the shortness of breath or cough.

I'm a 29 year old man with normal weight, and I am prone to anxiety, but never had anxiety symptoms present as persistent shortness of breath at all times of day. I have bad posture from being on my smartphone/PC a lot, including forward neck posture and rounded shoulders, and I'm wondering if that's causing a nerve to get pinched or something that makes it feel like I'm not able to breathe deep enough. I went to a chiropractor - against my gut feeling about them - and they did an adjustment and said it's indeed my misaligned spine and posture causing this, but I didn't feel any better afterwards and I'm skeptical that my posture's bad enough to make me feel so out of breath, and have a pins-and-needles sensation down my arm. Is it just anxiety making me hyperventilate? Do I need anti-anxiety medication? Will chiropractic help if I stick with it, or should I do a bunch of stretches/change my ergonomics? I am at a loss with this mystery condition.