I think that is actually quite a normal thing, plenty of people say things like "um" and "er" and "but" when they are talking. I think social anxiety definitely plays a role in things like that, I certainly found when my GAD was playing up that I had trouble communicating what I wanted to say. It's like being a rabbit in headlights. Do you find yourself talking more fluidly when you are comfortable, like when you are talking to your family?