Below is a list of things I've save in a notepad file exactly for threads like this. Here's a little history about my own issues.
It happened to me in December 09 during deadlifts. Like an idiot, I went on to do goodmornings and rows. For a couple of weeks, it caused the kind of pain that can make a person feel nauseated. It took 4-5 months before I was squatting my pre-injury max and 9-10 months before my deadlift max reached its pre-injury numbers.
Doing the things below allowed me to recover. Even today it bothers me but it continues to get better. On the bright side of things, I can now use tightness and discomfort in that area to predict the weather! Now compared to a few years back I have fewer flare ups, it moves out of place less frequently, it pops back in easier, and I don't have to put in so much damned work just to be functional and reduce pain to manageable levels.
In your case in particular, I would lay off the deadlifts. Pick a hip hinge that doesn't involve so much spinal loading. What immediately comes to mind are swings and dumbbell Romanian deadlifts but the choices are numerous. Deadlift covers a lot so you may have to do a few to several exercises to make up the difference.
You may want to lay off of back squats too. Maybe to front squats, zerchers, and/or goblet squats instead. You can still get really good leg development for just about any goals without squats and deads, you'll just have to be a littler more creative.
Below are the things I've done to make the issue manageable.
I've liked tractioning. I'll set up a band up high, loop it around my ankle, lie down with my leg at a 45 degree angle up and out and kind of wiggle my hip around until the SI pops back into place. I really only find it useful if it's out of place, but it can still nag you while it's where it should be just because of inflammation.
For long term SI health, I found using minamalist footwear like 5 fingers or the Adidas minimus to be very helpful. I was landing with too hard a heel strike to let it heal and this taught me how not to.
Clamshells might help shuttle blood in there and teach proper movement.
I like really light and easy goblet squats and 1 leg stiff legged db deadlifts. You're just trying to stretch things out and ingrain proper movement patters, maybe get a light pump sometimes but that's not even necessary.
Be sure to stretch out your piriformis. Also get a soft ball and work it into your entire hip complex. Stretch and do soft tissue work on your hip flexors. Sometimes they pull on your hip in a way that irritates the SI.
For SI the stuff on this link: http://thelowback.com/...x.htm#exercises The manual correction will work if you use a band set anchored up high too, just be sure to get the angle right.
These vids helped me too. For us weightlifters, you'll need to use a bit more than pressure from your hands. http://www.do-it-yourself-join...
I do this after first warming up the area with general light exercises. When my SI clicks out of place and I'm having a lot of trouble popping it back into place I'll cross friction by placing a broom into a corner and lean the tight ropy parts of my hip close to the SI into the round part of the broom and hold it gently moving it into there for a minute or so. I do this only if lax ball work and stretching and tractioning doesn't fix the problem because it does cause a good bit of inflamation and soreness and tenderness. The premise is that you're basically opening up tight tissue and reinflaming the area but having it inflamed where the SI should be so your body can build back the correct way. Followed by lying clams and very strict one leg db romanian deadlifts and bird dogs with a very slow tempo to make sure it's in the right place after loosening things up. Do not take anti-inflammatories. You actually want it to keep your SI there while it heals.
Google 'band man dave tate' and you'll see a couple of things for band tractioning for the lower back.