You sound a lot like me.
I tested negative the first time, and positive the second time. The tests are unreliable.
In view of your stomach pain, you should be seeing a gastroenterologist about a scope, and he should be repeating the tests for ifa and pca. It's taken me fully 7 months to get this far, and although I saw the specialist once at the start of July, no scope was done.
Instead, I agreed for the tests for PA and ferritin to be repeated. My ferritin was low, and the results of the PA test were overlooked (even though they were positive for pca). It was only my insistence on seeing them that brought the fact that I DO have PA to light - but it took nearly 10 weeks.
My readings could mean very little, but positive PA results should not be ignored in view of the increased risks of stomach cancer - sorry to be blunt.
Any kind of bleeding high in the bowel (innocent or otherwise) can go unnoticed and cause low B12/low iron. Ulcers, polyps, IBD, etc. can also be behind it.
The NHS is a shambles at the moment, and it is down to each of us to try to understand our condition and ensure that we get optimum treatment.
I've another B12/ferritin test on Monday, and it seems likely I'll be going back for a scope............. At this rate, I'll have been chasing around for 12 months before anything is resolved.
Incidentally, although your doctor will probably call you "normal" if they can get your B12 up to the mid 200s, internationally 500 is regarded as the healthy minimum. In Japan, where this applies, dementia is rare. The PA Society are campaigning for better testing and treatment here. God knows, B12 is cheap and safe to administer, and makes a huge difference to life expectancy. : )
Your GP should be prepared to give you sufficient cobalamine to resolve your symptoms, not just the "approved" dose. So don't be fobbed off with the "oh, we are just following guidelines" tosh. Warn them you'll buy extra ampoules from Turkey and inject yourself if they don't help. That'll shake 'em up! : )