I would also use care when you remove the mask and do it gently as diveray said. I sometimes find my students yank the mask to flood it quickly and in doing so force water up their nose. You might also try taking off the mask then sitting/standing in shallow water with your face underwater and breathing off the regulator may help as well in getting used to the water being in and around your nose, i .e, no mask breathing. If you want to conquer the problem, I have never had a student who couldn’t. Good luck.