Hey mad!
I had something similiar happen to Finnegan. A few weeks ago I took him to a dog park for the first time- he LOVED it. He ran and ran, and rolled, and licked and ran some more. After about 30 min I noticed he was limping a little- I checked his legs, didnt see anything and he didnt react when I squeezed and played with his leg. I assumed he pulled a muscle from running so hard. The next day was worse, instead of one leg, he seemed to be alternating limping on different feet. Again, I checked him out, squeezed and rotated his feet/legs and still, no reaction from Finnegan. It wasnt until later when he was sleeping, I saw the culprit- the pads of his feet were RAW! He must have ran so hard/so much he wore the callus's off the pads of his feet, poor thing. I put some hydrogen peroxide on them, and kept an eye for infection but luckily, he healed up pretty quick.
Meanwhile, it's now raining (again - tho I shouldn't complain knowing what the folks in the midwest are dealing with) and not sure when it's gonna quit, so may not be able to walk Finnegan tonight. Certainly hope to get a walk in tomorrow, if not later tonight.