How can I stop my hypochondria?!

I have actual hypochondria. It used to be that I asked my mom to take me to the doctors a lot. But now sometimes I can't leave the house because I hear people coughing, what if I get a disease from them? Sometimes when my mom takes out the trash I can't stand where she walked because she had the trash bag with her. Sometimes I can't sleep because I''m afraid something will crawl in my ear, of course the thought of that makes my heart pound and I think I'm going to have a heart attack! When ever I have a bruise I think that I have leukemia. I can't stand it anymore! I was hoping to go some where later but I can't, because there are people smoking outside. What do I do!?!