Crumbly bowel movement. Is this something serious?

I apologize in advance for the gross post, but I'm starting to get concerned. After being inactive for so long, I have been exercising a lot the past 3 weeks (mainly jogging). I've noticed for the past week my poop has been very crumbly. My diet has changed as I have been trying to eat lots of veggies and whole grains, but my poop gets getting more and more crumbly. Tonight it wasn't even all together like a log. It came out and looked like a a pile ground up lettuce. Is this normal? Should I be concerned? At first I thought maybe I was getting dehydrated from running, but I've been drinking six 16.9 oz bottles of water a day.