Hi AngelaMac,
Welcome. I am sorry to hear you have acute pain in your serratus anterior muscle. This muscle is nicknamed "the boxer's muscle." Most injuries and/or pain result in strain or over use of it. Do you do repetitive tasks?
If you've been researching you know that this muscle attaches to the ribs and the shoulder blades. It is key in raising the arm and assists in breathing. Often when the serratus anterior is inflamed or irritated you will also notice some pain with deep breathing. It can actually have similar symptoms to cardiac pain. Has this been true for you?
You might find this MH post dated December 2008 of interest and helpful. It's was answered by one of our Experts, Michael L. Gross, MD the CEO of Active Orthopedics & Sports Medicine. Here's the link:
http://www.medhelp.org/posts/Orthopedic-Sports-Medicine/Painful-Serratus-Anterior/show/712931
Here's a more recent MH Post that may not be as appropriate in your situation but it may provide some insight and useful information. This one was answered Dr Vinod.
Here's that link:
http://www.medhelp.org/posts/Orthopedics/Serratus-anterior/show/1150285
You didn't ask a specific question so forgive me for assuming there is one. In my opinion, any pain that doesn't respond to home treatments and lasts for two weeks requires clinical evaluation. I encourage you to consult your PCP.
Please keep in touch and let us know what you discover and how you are doing. Best of luck and I'll look forward to your updates. I hope this has been helpful.
Take Care,
~Tuck