Check sidysfunction.Com
or try google and use words: "sacroiliac joint dysfunction symptoms stiffness" and you will find something...

It sure sounds like a sciatic nerve problem. Maybe a lower disc is bulging and pressing on the nerve or the nerve canal (where it passes through the spine) is narrowed and putting pressure on the nerve. The sciatic nerve runs from your lower back along the buttocks to the outer side (and slightly to the back) of your leg. One piece branches off and wraps around to the top of the knee and the other goes right down to the foot then wraps around and goes to your big toe.

Bad sciatic nerve pressure will cause your big toe to be numb and there is pretty severe pain in the lower back, buttock(s) and down the leg. All kinds of odd feelings (similar to yours) will be present when it is mild and it could just be a nasty muscle spasm.

Sit on a bed and have someone gently lift your legs by the heel of the foot one at a time. Keep them straight but relaxed and see how high they can go. If you have a bulged or herniated disc, you will know it due to a quick sharp pain in your lower back.

Hope all works out for you.