Normal prostate size is 30cc, but many men's prostates start growing from age 25 and don't stop, so prostates can be up to 120cc, and that in itself is not a worrying issue (although it can cause difficulty peeing). If we correct your PSA for your large prostate volume, 9.8 becomes 9.8/100*30=2.94 which is just within the top end of normal, but a simple volumetric correction could be misleading (high reading could be due to an area of PCa (prostate cancer) in a prostate which normally produces low PSA), so whilst that reading could be OK, it also might not be OK. Also, you didn't cycle, or do strenuous exercise, or ejaculate, or have a digital rectal exam (DRE) in the couple of days before the PSA test, did you? That will increase the reading.
It's great that you have two PSA readings, but you missed out the crucial but of information - the dates of the readings so the doubling time can be estimated. The doubling time is much more important than the absolute values. If the PSA values are from last November and now, then that's a double time of 7 months, which absolutely should be investigated, and you should push to get that done in the 2 week cancer referral window. Unfortunately, most GP's know very little about prostates and prostate cancer.
The pain is also a flag, but there are many things that will cause such pain. Pain in the prostate is not localised and can feel like it's coming from the whole pelvis. Many people get back pain with age - mine which happened around the time I was diagnosed with PCa turned out to be due to a dehydrated disk, and nothing to do with PCa.
The only thing I can think about the MRI P3 is that it might mean PIRADs 3, which means they can see something on the images, but it's not obviously PCa. (A 4 would be probably PCa, and 5 would be almost certainly PCa, although an MRI alone can't tell for sure.)
Your symptoms would also match a prostate infection or urinary tract infection (UTI), some of which can be detected with a simple urine dip test - did the GP do that?
I presume you had a TRUS (transrectal) biopsy as an out patient procedure (done up the backside). A TRUS can't access the whole prostate, and this is even more the case with a large prostate. It might be that it could access the P3 area (if that's what they meant), but you should probably push the hospital for a transperineal biopsy, as that can access the whole prostate, and is more important for a large prostate, particularly where a TRUS failed to find anything before. A transperineal biopsy is also safer from side effects, but normally requires a general anaesthetic (longer waiting time for theatre slot, etc), although a hand full of hospitals are trialing a version which is done as an outpatient procedure like the TRUS.
So I think you should push your GP for a 2 week cancer referral. That doesn't mean I think it's PCa as other more common issues fitting your symptoms have not been ruled out, but there is a chance.
Also, it's useful for people answering questions if you create a bio in your profile, with dates of tests, results, etc. Then the advice is more accurately tailored to your specific situation.