Oh, Liz, I do sympathize! Health anxiety is utterly draining. I don't ahve any really good strategies because it's still kind of new for me, but I have recently been getting some calmness back by making followup appointments with all my doctors to ask all the questions that don't seem to occur to me -- or don't initially worry me -- when I first hear their diagnosis (even if it's that I'm fine). I'm so glad your doctor seems supportive - trying to assure you that there is nothing he thinks is life-threatening, and encouraging you to get further opinions and advice to help ease your mind.
I also take my boyfriend along to all my appointments. I claim he's my second set of ears. When I'm home freaking out about my health, I can ask him to sort of replay the doctor's advice and comments, and that makes my own memories and feelings about them clearer. If he couldn't go, I think I'd take a tape recorder.
I have also gotten into the habit of telling my doctors I have a great deal of anxiety about the issue, and could they please tell me one more time that there's nothing going on that can kill me. By the time I've asked that three times (SERIOUSLY) in an appointment (bless their hearts, my docs are all SO patient about this), it sinks in just a little, and I trust it a tiny bit more than I did before.
It sounds silly, and I'd be embarrassed if I weren't far more worried about just being able to function! If looking a little foolish helps me operate like a normal human being, call me Bozo the Clown and bring it on!
Hang in there, Liz!