First, I'm a writer, not a doctor, but health issues were one of my "beats" for years. I've corresponded with the world's top researchers on e-smoking, so I guess if anyone can hazard an educated guess, it's me. But here's a problem.
If a new condition appears soon after a new practice is started, then it's easy to blame the new practice -- even when there is no cause and effect. Some new e-smokers come down with colds, for instance. No relationship. Coincidence of time. That's all it is. But they might blame e-smoking. Wrong.
Your pain is probably an injury to the muscle. That doesn't mean it IS, but you're almost unique among the thousands who e-smoke. A few have reported LUNG pain, but not chest wall pain.
There are three other possible explanations:
1. Nicotine does cause a brief paralysis to airway muscles. That causes a gasp for air, or even a cough to relax the muscles. This seems unlikely in your case, but lower nicotine might help.
2. You are allergic to propylene glycol. Again, not likely. If you are, you can order liquids that uses vegetable glycerine instead of propylene glycol.
3. Propylene glycol breaks down in your body to lactic acid, the same stuff created by tired muscles. It circulates in your blood and can create a "sore muscles" feeling or even joint pains in some.
Unless the pain is debilitating, you can just experiment with not e-smoking, or e-smoking lower nicotine liquid, and see if it goes away. If it's a muscle strain of some kind, it should disappear on its own in a short time.
