I had the same problem... The biggest aid was the desire to dive!!! I just kept repeating it, "I want to dive... I will overcome this... I’m going to dive ... No matter what!!". Over and over and over again. Don’t tell anyone but I would walk around with my mask and snorkel on at home, just forcing myself to get use to breathing through my mouth... I was a nose breather too :) 135 logged dives now:)))