Not getting proper oxynation? You can try cold packs or warm compresses when sitting or really, just stretch. Stretching should help the stiffness. Do you think you might have arthritis? Do you have any numbness or tingling? That would be a sign of a different issue more related to diabetes (neuropathy).
It could be a lot of things, unfortunately. Could be the way you're sitting, even. You don't say what type or how much exercise you do, it's possible for example if you're doing leg lifts you have got a bit of an injury there. Could also be pinched nerves coming from your hips, meaning you might have a hip problem. Could be coming from your lower back, same thing, pinched nerves. It's impossible for anyone here to know given how little you've said about your lifestyle, but of course diabetes does lead to nerve problems if you don't keep it well under control (which you can do with Type 2). The back of your thighs include the hamstrings, and you might test by doing a hamstring stretch -- there are a million of them -- if it feels really tight or hurts to stretch. I have hip problems, though apparently not arthritis, and I have the same problem you have and a lot worse or a I wouldn't know about that possibility.