Postpartum shortness of breath

So I’m currently 4 weeks pp & I’ve been having shortness of breath and no other issues , I went to triage the other night and was there for hours they did test and said there is nothing serious wrong and that they don’t know what’s causing it & then yesterday all day I felt fine barely got short of breath any and then tonight it started again , idk what could be causing it . Is shortness of breath just a common thing after pregnancy?