Probably from the fibromyalgia I have it to

Happy birthday month! I don't know about Fibromyalgia, don't have it!
I call them strained or pulled muscles. My Dr told me they are muscle spasms from the little muscles in-between the ribs that help us breathe. I get the on the lower ribs in front and side, sometimes in the back. It helps to rub them out. [Sometimes I use TheraWorks for muscle cramps.] He has me doing upper chest exercises. Lifting a 5# hand weight up above my head and out to the side and front shoulder high. Then also doing some deep breathing exercises. I do the daily now along with walking. That has helped a lot, so exercise is important for us. Now sometimes when I have a bad coughing fit it will still give me a twinge, just rub it out like a sore muscle. That is what works for me.