Feeling pain after few hours is pretty normal, not like u feeling pain after half hour walking.

But having pain in the leg can be potentially shoe problem. you probably need to find better shoe. I'm not sure about Crocs, perhaps try sport shoes and see if u feel any better?

To track ur progress, u can also carry a small note book with u to note down the type of shoe u are wearing (brand, shoe type, etc) and number of hour/minute u started to feel tired, uncomfortable or pain.