Could be a lot of things.
If you're using cartridge razors and have fast growing hair, then waiting a day or two between shaves can actually be counterproductive. The blades clog easier, so you're effectively dragging the cut hairs across your skin, further irritating things.
However, back when I was using cartridges, I found that skipping a day was essential for going ATG, so it also depends on which direction you typically shave.