Hiya Cola!
You've been given a lot of great tips already! I don't want to overwhelm you with too much more so I'll summarized what I did that has helped me.
When I was diagnosed a year ago I had a LOT of GI problems as well. My doctor put me on an elimination diet and slowly over time I found out what were my trigger foods and what I could tolerate. I keep a medical journal and make notes of what works and doesn't work, then periodically review it to see if there's something I need to change.
As far as cooking goes, my crockpot is my friend. Load it up, go off and do whatever for 6-8 hours and BAM! Meals for days! I would suggest spacing out the meal prep, giving yourself ample breaks in between, then load up the crockpot and let it make easier meal-making magic!
Also - there's some companies out there, like Relay Foods, that will deliver organic produce to your door. It is a little pricey, so investigate and see if it's available (or similar service) and would work for you. But that's another alternative as well.
I've found that trying to stick as close to nature helps for the most part. Although, some things still give me problems in their natural form - like unfermented soy. Can't have edamame (problems for DAAAAYS) but miso soup is ok. *shrugs shoulders*
Hope this helps!