With you talking about blisters from your shoes and walking even an or so is giving you issues. If you are relatively healthy otherwise the issue sounds like it is probably a combination of what you are wearing on your feet.
First you need a good pair of Athletic Shoes, ones that specifically made for walking or running would be best. If that is not possible, then ones like Cross Trainers, or even Basketball(Court) shoes would be okay. If you are concerned about your feet getting hot, then you may prefer running shoes as they are often lighter. If your sneakers are something like Converse, Keds..or any other "flat" shoe you may find yourself having issues.
Next..Socks. Yes, you need to wear socks to give yourself that extra little bit of cushion. If you don't usually wear socks then even just a short pair of "anklets" is again better than nothing.
Then once you get the shoes, don't buy them the day before. You need to break them in before you do a major amount of walking. Even just wearing them around your house for a few days would help.
Some other things that people don't often think about. Stretch and "warm up" before you start your day. Stay hydrated, one cause of cramps and leg pain is not drinking enough water. Personally I bring a bottle of water every time I go and just carry it around with me all day, refilling it as needed.