i have a similar reaction 2 urs that caused my chest muscles to stretch. my mom told me to take ibuprofin and put a heating pad where the chest muscles are stretched. just relax and chill, dont do anything that'll cause a huge amount of stretching because that'll make it worse.
hope u feel better! <3
Hello!
Most probably it might be your pectoralis chest muscle. I would suggest you to rest, apply ice packs and take anti inflammatory medications.
If this does not help you would need a thorough examination near an orthopedician.
Take care!