What’s wrong with me??

I can’t go in a store by myself. I always try to work myself up into going in a store but end up failing and go home without getting what I needed to get. I’m scared that I’m going to embarrass myself my voice gets shaky when talking to a cashier. I really hate this because it prevents me from handling business and getting stuff I need. If I go in a store I have to have someone with me and my mom don’t be feeling like going in stores with me. I’m too old for this I’m 18 and shouldn’t be scared to go in a store alone. UUUGGGGHHHH