Stuck in a rut

The week before I joined my running club I ran a 5km race at Yokota Airbase and finished in 18mins 01seconds. Soon after joining the club my 5km time PB dipped to 17.55, then 17.49, then 17.45 and after a pause to get over an injury I ran a 17.33, but my most recent 5kms are boringly similar 17.51, 17.51, 17.55, 17.59, 18.10 and today 18.05.

I dropped my house key in today's race and had to double back and pick it up, but even if that cost me 6 seconds it leaves me lingering in the high 17s again. I think I'm stuck in a rut.