C.V.
Sounds like sciatica to me. Have you been gardening or doing other chores which require lifting or twisting?
The sciatic nerve is the large nerve that runs down the back of your leg. When it gets pinched (most commonly by a bulging disc), even slightly, you'll feel warmth, burning, tingling, pinching, even intense pain down the back of your leg.
Since it's very mild at this point, I would suggest that you take an anti-inflammatory, rest, have a nice hot soak, and take it easy on any lifting or twisting of the spine. Should the symptoms continue, I advise a visit to your doctor to determine the cause.
Protect your back by using proper lifting techniques, please!