For the last 5 days I have had a really dull pain in my upper left chest. It's not causing me pain as such but it's more of a discomfort. Then today a pain under my left armpit began. I'm not sure if it is muscle strain as I've recently been doing boxfit once a week. But it doesn't hurt with movement. It's just there and then it goes and then comes back. Not sure if anxiety is making it worse too.