Okay, there are a few reasons why PSA may jump around - the reassurance is that your PSA falls as well as rising which wouldn't really happen with prostate cancer. Episodes of inflammation, prostatitis, urinary tract infections, etc would be the most common cause of a PSA that goes up and down. But in your shoes, I would be asking the urologist whether it is time to have a DRE; I think the NICE guidance is that men on AS should have one every year.