I don't mean to sound rude, but '19' is no age to speak of... I'm 40, and my stutter can still puzzle me sometimes. At any rate, stutter is known to vary (in many aspects). That's probably something you could work on getting used to. It takes time to get to know yourself in this way, and it's never quite certain, but it helps keep the surprises down. Perhaps speech therapy could be beneficial to you. Might want to give it a shot, if you can.