Hmm, past gallbladder problems and having been pregnant. You know that makes it worse, right?
I suggest you get your gallbladder checked out again. If a ultrasound is clear, go in for a HIDA. Hopefully it's as simple as that.
There's also the chance that your intestinal flora is messed up, in which case eating yogurt with active cultures or talking probiotics may help a little.
Whatever you do, don't let anyone pass you off as IBS. You need to have IBDs ruled out (as those do damage). Make doctors actually do their job instead shrugging you off. I've, frighteningly, come across several stories of people with pancreas problems that were misdiagnosed as IBS simply because the enzymes looked good when they weren't having attacks.
Some things that may help a little. No sugar or anything with high fructose corn syrup in the morning - the HFCS is hidden in a lot of stuff, so no premade breakfast foods if you can help it. Sugars, especially if you eat a lot of them, can cause osmotic diarrhea (too much water gets drawn into the bowels).
Try a protein source + complex carb. It'll take longer to break down and won't turn to sugars so quickly (like simple carbs do). Try taking or eating something with a lot of fiber during the day. Don't eat a big meal for dinner, you have to digest it and evening tends to be a time when some body functions settle down (has to do with one's circadian rhythm).
And for extra fun, go low fat and see how that helps. When you're cramping, you might even go no-fat those days. Replace your milk with lactose free or (cow) milk alternatives - be careful with fat-free types, though, as they sometimes have sugars added.
These are just some things that have helped me a little. I had my gallbladder out a year ago and unfortunately I'm part of the percentage that didn't get rid of the diarrhea issues.
Be careful of taking stuff like imodium, as well. Long term can't be good.
Don't be afraid to go to a GI doc. There is the possibility of uncomfortable test, though nothing as bad as giving birth.
This isn't something you want to keep happening because it will start affecting your electrolyte levels, along with other vitamins and minerals. That's the last thing you need with chronic migraines.