Ask for a percent free psa test. That will either be suggestive of cancer or it won't.
Read here en.wikipedia.org/wiki/Prostate-specific_antigen#Free_PSA
and note the chart on the right hand side.
At a minimum I would do a retest in 3 months rather than six. The worry is that a fast moving PSA in a young guy can be a sign of an aggressive cancer and if that's what it is you don't want it to slip out of the bounds of curability. First thing to do is rule out an infection as other posters have said. Get a dre if you haven't had one. Next thing is free PSA test, a cheap quick blood test. Find out the size of your prostate (which is evident on the ultrasound images used to guide the biopsy.) If the prostate is unusually large for someone your age, then the PSA might not be as concerning, but if the prostate is small or normal size, and the PSA is high and rising, and infection has been ruled out then further testing is in order to find out what's going. False positives happen in biopsies.
** I am not a doctor. My opinions are not medical advice. **
DX age 54 9/2012 PSA 5.3, DRE-, high PSAV. Clinical T1c
Biopsy: Gleason 3+4 with PNI / PC in 6 of 14 cores / 10% of length
Tx: RRP 2/2010
Pathology: pT2cNxMx / G 3+4 / PNI+ / SM- / SV- / EPE- / Volume 3cc /
PSA in 2010: <0.01 | 0.01 | 0.01 PSA in 2011: .01 | .02 | .02 | .01
PSA in 2012: .039 | .039 | .043