Mine lasted for years - it's so frustrating, isn't it? Mine was shooting pain that occurred for (seemingly) no reason, and I would often lose my footing when the leg gave out. The pain started in the buttock and then shot down the leg to about the knee. For me, it was only on the right side but a lot of people have it bilaterally. Pain relievers do very little especially because no pain reliever addresses the cause, only the symptom. They are okay for a temporary problem but not something chronic.
Several things can help. Some people find that chiropractic care and good massage therapy (by someone trained, not just someone rubbing your back) can provide relief. Usually a massage will not "hold" if the alignment is off, which is where chiropractic comes in. I did this for years and spent a lot of money, with some relief but not complete.
Yes, lying on your back with your knees up is a good exercise. Do it frequently especially when you are NOT in pain. But while you're there, press the small of your back into the floor so it's flat and not arched at all. To do that, you have to contract your abdominal muscles. Try any exercises you can to strengthen your abs - do controlled and slow crunches (not full sit ups!) just supporting your head/neck with your hands but not pulling on the neck. Let the abs do the work. Slow, gentle, just to get your shoulders off the floor. Don't tuck your chin - keep your eyes looking at the ceiling and just see if you can get the shoulders up (but the back, from the bra strap down to the waist) stays flat and pressed into the floor. Do a set of 8, rest 5 minutes, do another set of 8, rest 5, do a third set of 8, stop. After a week (sooner if you can), make the sets 10 repetitions. Another week, 12 reps per set. But still stop after 3 sets for at least a few hours. If you belong to a gym, you can get some help from a trainer to work on other ab exercises but for now do NOT do anything where you raise your legs from floor to waist.
You can also bring your legs up while lying on the floor so that your thighs are close to your chest. Gently hold your legs but don't push down on them - put your hands behind your bent knees so they are on the backs of your thighs and your calves are just gently lying on your hands. Does that make sense? Fetal position but you are on your back. Now GENTLY roll a little from side to side, massaging your back.
These things can help but will not likely get rid of the problem.
I finally got rid of things entirely when I started a good supplementation program with a comprehensive formula that provides cellular health - not just all the regular multi-vitamins I had taken for years or all the stuff from the health food store. Spent a fortune, got no absorption and no real results. There is great new research on a natural anti-inflammatory that also helps with cell repair - there are many many published papers on this and it's all food, no drugs. If you'd like some links on that, let me know. You can buy it on line but you need to get some education from a consultant (free). That has made all the difference for me, for this sciatica and also other conditions. I'm pain free and haven't been to a doctor in years except for regular check-ups. My physician is thrilled with my lab work as well as the fact that I'm never there!