Oh dear, sorry to read that, Meg,
I might recommend some Robaxacet, (muscle relaxant + Acetominophen) which is available OTC here in Canada, although I think it requires a prescription in the US. Since this is a sudden onset pain, and not likely a result of an obvious injury (like spraining an ankle, being in an accident, etc.) I would guess it’s more likely to be a spasm of some sort, rather than a tear or strain which would cause inflamation, and for which Motrin / Advil / ibuprophen would be more appropriate. Also, moist heat (warm bath, pad, shower) or a massage might help with a spasm.
I would suggest that if this makes it more difficult to breathe, such that you have to “think” about drawing breath, or if the pain does not go away in 24 - 36 hours, or if you feel weakness, numbness, a buring/fire sensation, or tingling, that you see a doctor sooner rather than later.
Please bear in mind that I am not a medical person, do not have any formal medical training, and that free advice is worth every penny you pay for it.
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Best of luck, get well quick.