The good news is that your PSA continues to fall while on Proscar. That tells you that you have some BPH that the Proscar is helping to eliminate, and you're also peeing better probably. The Proscar is making your PSA a much better indicator for prostate cancer, and as long as it goes down or stays stable, there are no red flags.
Free PSA is affected by BPH as well as PC. It's the Percent
free PSA that matters, not the free PSA. Because your PSA is going down too, your % free PSA is still within the normal range. There is a more accurate blood test called PHI. You can only get it from certain urologists. Call the number at the link below to find ones near you.PHI
There's a urine test called PCA3 that is only covered after a first biopsy (which you've had) and if suspicion remains (which it probably doesn't in your case). Get pre-clearance if you decide you want it. There are other biochemical tests, all much more expensive and none of them covered by insurance or Medicare.