Thigh/hamstring pain, no apparent reason...?

I got up from my desk yesterday at work and felt a slight discomfort on the back of my right thigh. Didn't think much of it until I got home, sat for a while, then got up again. The pain got worse over a couple of hours and my thigh felt hot to the touch (no swelling or bruising, though). It hurts when I bend forward (with my leg straight or the knee slightly bent) or whenever the muscle flexes a bit, kind of like sharp pulling. A day later, whenever I get up after sitting for a few minutes or longer, I also feel an odd pop in the tendon on the back of that knee, and it feels slightly sore.

It doesn't actually hurt to walk if I don't take particularly long steps (except right after getting up, but it passes after a few minutes). I haven't been doing much of anything in terms of sports or any strenuous activity, haven't pulled or torn anything that I'm aware of. The pain seems to have started all on its own. I have no history of lower back pain. Should I be worried? Is this something I need to see a doctor about?

Thanks in advance for your replies. :)