What is wrong with me?

I can't leave the house without the fear of getting out somewhere and having to go to the bathroom, so I avoid most all outings, at all costs. Days before an upcoming event that is going to require I leave the house I stress over it so much I stay sick with the diarrhea the whole time and end up having to cancel because I'm stuck in the bathroom. My anxiety during these times if often unbearable, I can't sleep, eat, and all I can think about is how many ways I could end up embarring myself by leaving and actually getting sick, or my worst fear, actually messing myself. I should be in high school right now, but instead I'm home schooled because when this started I had to be pulled from school because I missed so much. I feel like my house is the only place I'm safe because I know my bathroom is right there if I need it. I've tried many times to just be a normal teenager, but every time I leave the house to go hang out with friends or anything I can't enjoy myself at all because I'm so anxious and I end up getting the diarrhea and having to rush home. As soon as I walk into any social setting my mind automatically starts figuring out an "escape plan", in case I get sick and need to leave quickly. I always check the bathrooms at every place I'm at to make sure there are secluded and have a loud fan or some sort of loud background noise. It is just completely crazy the things my mind cooks up. It's so embarring and I feel so alone in this world, because I don't know of anyone else who is like this. It's getting so bad to the point now where I won't even go to the doctors or dentists because I get so sick in anticipation. I am supposed to see a therapist weekly, but I only make it in about once a month, if that. He seems to think this all comes from an abusive childhood, and that I'm doing it to protect myself from letting anyone close to me. I can see where he's coming from but I think theirs more to it than that. I really don't know what to do anymore, I'm at my wits end. Help please. And please no rude answers. This is very hard for me to even talk about so please keep your hurtful comments to yourself.