Is there any way to add pasta to soup without the pasta doubling in size and getting mushy in the fridge later.I've even tried putting uncooked pasta in with the same result.
If you're going to hold soup with pasta in the fridge, store the pasta separately, and add it when reheating the soup. This also goes for soup with dumplings.
This does mean that you'll need to cook the pasta separately from the soup, which is another pot. If you look, though, this is what a lot of recipes recommend.