Speaking of new shoes... minor setback

[demandypants]

So I got fitted at the local running shoe store last week and took my first run in them on Friday. about 3 miles. My feet felt fine, i just had a little lower back pain. But I had been a little sore last week anyway from Monday yoga that kicked my butt as I had a 6 week break from that. So I didn't think anything of it. Well by sunday i was crying in bed because my whole left leg was cramping - Sciatica, pretty sure it was caused by my piriformis muscle and not a spinal issue.  Anyway, I am recovering from that. Stretching a few times a day. I still can't feel my left foot 100% but most of the pain has stopped.

How do I test out my running shoes again?  Do I need to take shorter runs? Or was this more of a result of not cross training enough to keep my piriformis from being literally a pain in my ass?  Any suggestions on preventative measures to keep this issue at bay?