A vaccination, like any other medication, can sometimes cause side effects - fortunately, they are often mild and pass within a few days.
Having a blocked bladder (being unable to pee) is an emergency and can cause death if left untreated. Contact your vet for an emergency appointment if your cat is struggling to pee.
Cats don’t often eat things they shouldn’t, but occasionally curiosity gets the better of them and can lead to a blockage. String, thread, hair bands, rubber bands and tinsel are the most common items to cause a gut blockage in cats.