I am sorry that I keep forgetting to measure my cranks - I am 5'2" and my bike is a 2011 46cm Bianchi Via Nirone Dama 105 (That's a mouthful!). I presume it is 170mm....

My update - after being off the bike for nearly three weeks due to travel, I did 18miles last Friday and 21miles last Sunday with no issues.

So maybe I just need to ride more - more often at less distance perhaps than the 40- 50 miles that I had been doing at a stretch.