My thoughts and feelings get the best of me ?

I'm constantly being over ruled by my thoughts and feelings how do you take control and ignore them especially if they are all negative and don't get me anyewhere. They usually have to do with getting myself to start excercising so I can feel better about myself and feeling like I'm always being judged because I feel like I have a weird resting facial expression or its an expression I'm making because I'm nervous. Those and a combination of laziness are keeping me from being happy. Does anyone know what I should do maybe some tactics I could use?