I'm resurrecting this old thread by way of follow-up, in case it might help someone else. To summarize briefly, I've been dealing with a chronic condition that, for the first 10 months, did not exhibit any visible symptoms. I'd fired one doctor and my new primary care doctor ("New Doctor" in the OP) did not appear to believe anything was really wrong, so I was asking for strategies for dealing with him.
The advice below offered by cicero and several others proved to be quite effective:
first - write everything down on index cards. your whole history in bullet points.
I made a Word document that contained a list of my symptoms from month to month, including anything I found that made them better or worse. New Doctor didn't care that much about it, actually, but discussing it helped to get me referred to first a neurologist, then a rheumatologist, then a hand specialist. The specialists thought it was the best thing
ever, since it showed the big picture (I have symptoms that at first glance appear to be unrelated) and I didn't have to rely on my memory to tell them which symptoms showed up when. The rheumatologist was so excited about it I thought he was going to frame the darn thing.

Apparently patients who don't remember when symptoms started are a big problem.
The document, a calm, logical approach*, and persistence resulted in a diagnosis just over a year after the first symptom showed up.
* This approach worked for me. I can totally see, however, where crying or otherwise expressing frustration could be the key in other situations.
So I started out thinking I had a urinary tract infection and wound up with a diagnosis of inflammatory arthritis (probably psoriatic arthritis minus the psoriasis). I fall into a small percentage of people in whom the condition is not reflected in lab results.