It sounds like a lab error. Ask for a PHI test next time (it includes both PSA and % free PSA).
If your PSA is explained by your enlarged prostate, and there is no clear pattern, so I don't really see the cause for concern. A useful marker is PSA density = PSA/prostate volume -- it should be around 0.15 or less.
Allen - not an MD
•PSA=7.3, prostate volume=55cc, 8/17 cores G6 5-35% involvement
•SBRT 9 yr onc. results
•SBRT 7 yr QOL results
•treated 10/2010 at age 57 at UCLA,PSA now: 0.1,no lasting urinary, rectal or sexual SEsmy PC blog