Concerned about a spike in PSA level

Dear Doctor,    I am 58 years old and have been getting annual PSA tests for 10 years - always tested in Nov-Dec of the year.  (My father had Prostate Cancer.)   My PSA levels between 1997 and 2003 were between 1.7 and 2.1.   In 2004 and 2005 they were at 2.8, and back to 2.4 in Dec. 2006.   My DRE always showed slightly enlarged prostate, but no lumps.   Then in August 2007, my PSA spiked to 9.34.   My Family doctor suggested monitoring it.    In Sept it was 6.82, Oct = 5.93, Nov = 5.76 and Febr 2008 = 3.67.    My Family doctor recommends to continue to monitoring my PSA at 3-4 month intervals.  Should I be concerned and taking more aggressive action?    Is this normal to see such wide swings in PSA levels?