I injured my back a couple of times during my 28 years in the Navy, the last and worst in '83 while serving on a destroyer in Pearl. I haven't had too many days without pain since then and I'm legally disabled with a VA pension, mostly because of that. I have been treated with everything but surgery so far and I'm not going for that until the pain gets lots worse.
Here's my $.02, FWIW:
As already explained, the sciatic nerve is a big nerve formed by the combining of several nerves that exit your spine in your lower back, come together to form the sciatic nerve and run down into your leg, branching out as they head for the toes. The pain in your leg can usually be traced to an "injury" to your lower back. This injury is really a squeezing of the soft pad between the vertebrae, which pooches out and bumps up against the nerve. The vertebrae are the 4th & 5th lumbar and the 1st–3rd sacral, down low. Since nerves really don’t like to be squeezed, they get angry. The immediate pain in the back at the point of the initial injury, is then followed by pain, itching, tingling and sometimes reduced mobility down in the leg. A typical sign of a pretty good impingement to the nerve in the lower back is a painful tingling in the quadriceps muscle area, sometimes down to the knee. Depending on which of the vertebrae are hurt, you may have pain and tingling all over your leg and butt. The symptoms you describe are classic. Mine comes and goes when I forget that I have a bad back and try something stupid. Once injured, this problem will most likely be with you for the rest of your life…but it is treatable.
Go to an orthopedic surgeon for consultation and treatment. Stay away from a chiropractor until you see the real bone crusher. You may have something wrong that the chiro could exacerbate with his "adjustments". The doctor will take x-rays, and may recommend an MRI, then explain what is wrong and recommend a treatment plan, which may include an anti-inflammatory drug like Ibuprofen.
And finally…stay OFF the drugs until you see the doc. You’re likely not doing yourself any favors self-medicating. The sawbones can really help you out there. He/she may prescribe PT, pain drugs, simple exercises, or even surgery…but chiros and drugs now are probably not a super fine idea.
There's plenty of info on the web too...but I still say go visit the doc.
Good luck!