I would have to see you do this to be sure, but it sounds like you might be confused about how you are exhaling. I have seen many students who cannot really tell whether they are exhaling through their nose or mouth. This is most common with people who exhale forcefully through their regulator (mouth) when they are trying to clear their mask, but you might be doing the opposite; tht is, you may be exhaling forcefully through your nose when you are trying to clear your regulator.
I gather this from the problems you are having with your mask while you do this--it sounds like you are breaking your seal with a nose exhalation.
I gather this from the problems you are having with your mask while you do this--it sounds like you are breaking your seal with a nose exhalation.