I feel the same as you...I have seen so many doctors, probably 12 in the past two months for various illnesses and have had countless CBCs, probably around 7, and have talked to so many nurses. I've had ultrasounds, pelvic exams, my neck touched by 5 doctors even specific blood tests. Everything is always perfect and say I am in perfect health..yet, I fixate on the thought that they all must be wrong and I must be right. Quite ridiculous actually, when doctors with so many years of experience tell me I'm fine yet I think I know better, when I don't even have the symptoms for half the diseases I worry about.
You need to trust the doctors, Its easier said than done. I wish i could too. There are days when I realize I'm fine and I'm so happy, then a few hours later, I'm Herr again, worrying about the same dumb illnesses.
My doctors have told me that if anything was seriously going wrong , USUALLY (not always as some cancers and diseases do not show up in the blood), something would be off in the bloods to indicate an issue. Its not like they can say yup low iron , you have ______cancer. But blood tests are a decent indication that you are probably okay. Otherwise they wouldn't even do them.
But pantsy is right, its the doctors word that are more important. If you've seen so many, they come in with an unbiased view. its possible one doctor can be wrong, maybe two, but so many? Basically impossible..