Several years ago, I had an issue with my sciatic nerve. My piriformis muscle was getting irritated and every time I would stand up or sit down I would get the most painful cramp in that muscle (it's underneath your glutes near your pelvis, so basically I had a pain in the butt). It was incredibly painful. I was having trouble walking, getting in and out of the car, and just doing life. I also had issues with numbness in my foot/ankle and on the outside of my knee. But it was only on one side, not both legs. The sciatic nerve runs through the piriformis muscle so my symptoms made sense. If you have any numbness or unusual tingling, that would be a good indication that the sciatic nerve is involved. I'm not a doctor, just offering up my anecdotal evidence.

By the way, the doctors at the time had basically no clue what was going on and treated me like I was crazy or drug-seeking. Fun time. I was ready to kill myself if it had gone on much longer because it was so intensely painful.

ETA, my back didn't hurt either.