Are you allergic to shellfish ?
From years of loving the stuff and making it my go to food of choice (mussels/frites and fruit de mare etc.) I seem to have now become allergic to it. It takes a couple of days to manifest itself so try looking back to something you ate a few days ago.
Nothing will eleiviate the vomit nor general unwellness, you have to let that pass but it clears up after a couple of days, and yes it makes my legs hurt too.
I steer clear now, I have been told I may get over it but that's at least a couple of years away, seems something sets in your tum and takes that amount of time to dissipate.