Seeking expert counseling is a sign of strength. A personal relationship with a caring professional is proven clinically effective.
I believe that I can help you.
It seems that you have a somatoform disorder officially called hypochondriasis (or health phobia or health anxiety).
This means that you believe that you have or suffer from several disorders, which when tested, prove negative.
This is very similar to Obsessive Compulsive Disorder (OCD) except in the latter you worry obsessively about getting the disorder or passing it on to someone else..
They are similar and can be treated similarly, with cognitive behavioral therapy (CBT) or exposure therapy and also with medications (such as paroxetine/Paxil or fluoxetine/Prozac).
If your current therapist is not treating you with CBT and/or exposure therapy, or is not succeeding in stopping this behavior, then you might consider finding one who is more effective for you.
Also, speak to your doctor about starting a low dose of one of those two medications that I recommended, or tricyclic antidepressants such as clomipramine (Anafranil) and imipramine.
I wish you great success in getting a handle on a this disorder.
I shall keep you in my prayers.
Elliott, MAE, LPCC, NCC, CCMHC