It sounds like you could be pretty critical of yourself, I would see if I could learn to laugh at/with myself and help myself rather than get down on myself. Turn your hmms and mmms into a hum instead and smile, especially when you are with yourself (I know I would "think" hmms and mmms too when trying to talk to myself inside my head!) Practice making your self-talk pleasant, fun, funny, and helpful/supportive and being your own private cheering section when you are talking to others.

I would write out a little script about myself for introduction purposes, memorize and practice it a bit so when called on to introduce myself somewhere I have somewhere to start? I'd also play a "game" with myself where I would see how well I could add something "extra" each time (". . .and my favorite color is green!" :-)