Thanks for your suggestion, yes I usually exhale hard through the nose when turning to air....it maybe I'm not taking enough air in, when i breathe, I feel somewhat tense after swimming 50 ft
Try to blow out through mouth and nose, so that the "blow-out" will become a "nearly-all-out". Inhaling will happen by itself...
Surely there will be some tension in your whole body built up and helt while swimming your 50ft. Did you try with some balance-drills like Torpedo, Superman, Skate before
swimming in whole stroke? Breathing really is a not easy skill. Building it, you should be familiar with balance- and streamline-concepts.