unusual but harming me: plz help

Hi,
      I have a very bad situation right now. Actually a thought came in my mind about a disease few months ago that I would be having. I became so tensed and stressed that I decided to get tested for that. But online I saw some information about this disease kinds which are rarely and specifically found in some countries.  I got scared and thought I can get that kinds also which is not possible as they are found in some other countries and the test for that is also rarely available because it is rare. This all happened because I started finding information online. Even I know that rare disease kinds is not possible, even he specialist doctors also saying to me that I don't need test for those kinds as they are not found in this country. But somehow my mind is not accepting that(though I know that is wrong) but it pops in my mind and make me feel nervous and anxious. Due to all this, I hve developed headache and am not able to sleep. I stopped talking properly to people and think about this all the time. I on't know what to do. I am having depression and anxiety. I am not able to convince myself that that disease kinds are not possible. Even specialist doctors are saying then also.

I went once to psychologist, he just said to me that all wrong things I am thinking that even I know. That one visit didn't help me.

Is there a cure for my problem? I am very worried because I think how will I live with this. How will I work.

Plz comment on my situation.

Thanks and Regards