Does anyone know how to get along and appreciate my overprotective mother?

I may need a therapist. I don't know. My mom is extremly overprotective, and I'm extremely independent. She calls me between 1 and 3 times per day. If I go out shopping with my friends, she calls my husband and wants to know when I'll be back, where I am, who drove, and if he minds for me going out with my friends? She is driving me bananas, and I end up snapping at her on a weekly basis. I love her, and I want so badly to have a good relationship with her, but I can't stand the constant behavior police. I started a home show sales business, and now she is griping about how she worries about me being on the road at night, and how dangerous it is, and how my son needs me. Every day is a guilt trip of some form or fashion. I don't know what to do, I'm at my wits end. I'm 29, this has got to stop or it is going to ruin my relationship with her. Everything I do, is up to her to conduct her 20 questions, and then the guilt trip if I don't comply. pray for me, i'm going insane, and I'm sad.