Back again I'm afraid. Just to recap.

Welcome bqack to the Forum.  I note that this question is a follow-on to at least three other series of questions to Dr. Handsfield or me over the past few months.  I'll also not that 2 months ago I said to you  "Emphatically, your tests prove that your did not get syphilis from your misstep.  Further testing would be a waste of time and money."  Dr Handsifeld replied similarly regarding HIV.  Our advice however does not seem to have helped you to stop testing or asking for our assurance that your tests are conclusive which they are.  The doctor who suggested you retest in six months was being overly conservative and perhaps is not familiar with the scientific literature on test performance.  you do not need more testing.  Clearly however, what you do need to do is work with your counselor/mental health professional to confront what is likely the guilt which drives you to continue testing.  You also need to accept that you were not infected by your encounter out of your marriage and that your tests prove this.  EWH

I know I am probably coming across as a crazy person, I have been working on my anxiety, however this fear which is no doubt irrational keeps returning. 

Every time my wife gets a new pimple around her lip I freak out and think it must be the start of a syphilis chancre.

From what you have said I should be 100% certain I don't have syphilis or anything else I've tested for?

I got worried when the doctor said 6 months for testing, even the NHS only quotes 12 weeks. I assume 6 months is not an incubation period anyone works towards nowadays?

I agree with your statement, 6 months is far beyond ANY POSSIBLE incubation time for syphilis or, for that matter, any otehr STI.  You have to put this aside.  

Also, I must remind you that the forum does not permit repeated anxiety driven questions by the same users. This will have to be your last one and the thread will be closed later today; future new questions on this topic will be deleted without reply and without refund of your posting fee. This policy is based on compassion, not criticism, and is designed to reduce temptations to keep paying for questions with obvious answers; because experience shows that continued answers tends to simply prolong such anxieties, when the real answer normally should be professional counseling; and because such questions have little educational value for other users, one of the forum's main purposes. I trust you will understand.  EWH