Maby you can seek onother aproach than medication.I have been having psychological help with talking sessions and it have helped me a great deal with my anxiety problem!
I agree with pinkfloyd. Talk with a therapist to help learn techniques that will help break this cycle of thoughts. Also, keep yourself occupied as well. In addition,
take a moment to try to rationalize your thought process and think about whether this thought makes any sense. Try to replace this thought that comes in your mind with something you enjoy every time it occurs.