Depending on date in June, your first PSA test was in mid August and so early December is only 3.5 months gap. If so, not sure what the problem is - 'normal' is
6-8 weeks post op (surgeon's preference)
3 months after 1st post-op test
3 monthly up to 2 year mark and if low & stable,
6 monthly to 5 year mark then
annual for the rest of your life.
In theory, that means that your annual test will always be 6-8 weeks after the anniversary of the op.
If you are not happy with the wait to December, you could just ask the surgeon to bring it forward a week or two. If the PSA is going to be managed by your GP, you should be able to book the test at the end of November without anyone making a fuss. Not sure what benefit you would get from private lab testing in between times - it isn't necessarily reliable / comparable and your surgeon is unlikely to give you an early appointment or take any action based on its results. Just seems to introduce a new unnecessary level of angst?