Sciatic nerve pain, AKA sciatica, happens when the sciatic nerve is pinched, inflamed, or compressed. The sciatic nerve runs from the lower back at the base of the spine down both legs (pale yellow in the picture)…
picture from Wikipedia
Sciatic nerve pain can be caused by a traumatic injury (like a car accident), pregnancy (fetus putting pressure on the nerve), spinal disc herniation (most common), tumors and even carrying a thick wallet in your back pocket! (piriformis syndrome)
There may be others, but these are the ones I read about when I googled “why do I have deep pain in my legs between my hips and my knees?” I vaguely remember having the same problem when I was pregnant years ago, but sometimes I get this pain for no apparent reason.
My sciatic nerve appears to be affected by cold temperatures, cool and damp weather as well as swings in temperature. The pain usually only lasts for a day, but last weekend I was miserable from Friday to Monday. Advil helped, but as soon as it wore off the pain was back. A topical cream containing capsaicin helped, and I hear creams containing arnica do too but I have yet to try that.
This sounds horrible. I hope you see a doc and get a more permanent solution. Good luck.
Stretching can really help, too. If you Google some recommended stretches, you might find it useful. I had this when I was pregnant. I stretched, and I also saw a chiropractor. My father has this now, and he saw a physiotherapist, and was given a list of stretches to help with the pain.
(It doesn’t help when Mother Nature gets into one of her “moods” though, does it!!!)
Overdoing it with low impact aerobics can do it too. Two decades ago, while happily showing off how low I could go in a wide leg stretch, bending each knee to alternate going further down, I heard a sort of pop. Dang. That’s what I got for being cocky. Today, there’s not a cocky bone in my body but that day, competing with my brother, I got paid back. hmmm