I've found a couple things have helped me enormously: First I learned the bilateral breathing and now it feels so normal I don't know which side I use to use exclusively; second the interval training has not only built up my speed and stamina, its also increased my self-confidence that I can handle the intensity of the water; and third I use a pull-bouy, which helps me ignore my lower body and just focus on the upper, and also gives me a bit of the feel of being in my wetsuit.