Had soft ulna fracture last year. still experiencing pain when temperature changes. why does this happen and when is it going to stop?

Maybe: Unclear what a "soft" ulna fracture is? Patients often report being able to sense temperature or weather changes in their bones. I am unaware of any physiologic basis of this, though many people do report it. If the pain is severe, it should be investigated to rule out a non-union.

Will resolve: It can take a year or 2 until the bone fully remodels (reshapes). The bone lining is sensitive to pressure changes until the entire healing process is over.