I agree with the shoes too tight as the main culprit, especially if they are new shoes. It may also be that the interior padding is wearing out in older shoes, especially if you walk on them a lot (as an example, running shoes are only good for about 100 miles before the inserts need to be replaced).

Alternatively, it may be that you are keeping the weight on the feet, rather than lifting on the upswing. This may be hampering the circulation. Make sure you are lifting on the upswing, instead of pushing up with the downforce of the other foot.
Note: I had that problem on an elliptical trainer at the gym (where the feet are always in contact with the pads).