I'm with 3.30 or bust on this one. Piriformis syndrome sounds possible, and it can have lots of causes, including wrong trainers, not stretching enough, and doing too much too soon. A quick google will bring up lots of info and treatment suggestions. I suffered with it on and off for ages, but it is sortable.
Oh, and that's a pretty smart time for a first 10k off a couple of month's training. Well done, and don't give up!