After having a pulmonary function testing & spiro breathing test done, nothing showing obstruction. i'm constantly short of breathe. what's next step?

Short of breath: You need to have cardiac work up done.Shortness of breath can be due to some heart disease as well as pulmonary condition.You need a chest xray to rule out lung disease beside pft and spirometery, sometimes you need cat scan to rule out pulmonary embolism.And for heart you need an exam, ekg, echocardiogram and/or sress test to find the cause of your shortness pf breath.

Rule out other cause: I would also suggest that they rule out restrictive lung disease. This may be detected as well by pulmonary testing.