u/Hot-Spite-9880

I adopted this sweet girl a month and half a go from a local animal shelter the owner had to give her up for some reason or the other. I noticed the sac on her and was told she was probably pregnant at some point though the shelter didn't know when. she was of course spayed and all that. after 3 to 4 weeks I went to the vet for a physical and said it was nothing to worry about. well its been another few weeks and its still there... generally how long does it take for swelling to go down? and should I get another opinion?