Disease and infection related phobia.

I have various disease and infection related phobia. Every time I check myself weather I am feeling any pain in my chest or not. Regarding any blood test or injection I always think that the opposite person has changed the needle or not. Again and again I just want to take the reassurance by asking him. If I come in little close contact with any street dog, I always think that I may get rabies. One mind always thinks that nothing has happened, if I catch any dog bite or scratch then of course I should feel that. But the other mind always tells me that something wrong has happened. So I need to check my leg again and again, need to check my cloths and jeans, if there is any marks that I am missing. It's really very difficult to deal with this situation. I am loosing my body weight also. This situation is constantly hampering my peace of mind.