I'd be cautious with a food journal. I used to be phobic of many foods. The problem was that I started seeing patterns that weren't there: I'd feel ill after eating, and attribute it to the food I'd eaten, when actually I would have felt ill anyway, whatever I'd eaten.
My phobia was also made worse by reading so many websites, and from seeing nutritionists, who told me that this or that food was "bad". Nearly every food will have been declared bad by someone!
I ended up in a situation where my diet was extremely restricted, and I was losing weight when I was underweight already.
It's tricky because many people with IBD do have trigger foods or do well on a certain kind of diet. I eventually figured out that avoiding much fibre meant a significant improvement in my symptoms.
If you're getting afraid to eat, I would advise you to steer clear of any very restrictive diets. Concentrate on what you can eat. There are some foods that are usually well tolerated - the "BRAT" diet, standing for "Bananas, Apple sauce, Rice and Toast may be a starting point. Have you been tested for lactose intolerance and coeliac? You could also ask your doctor for supplements - they usually come in the form of something like milkshakes - Ensure, Fortisip, etc. These are usually well tolerated (though you might want to check whether some contain dairy) and are high calorie so should help you gain some weight back. They also provide vitamins and other nutrients, which may be especially helpful if you find most fruit and vegetables give you problems, which is quite common. They save you from having to fill up on lots of low calorie fruit and veg.
Remember that being underweight carries health risks, and not eating enough could make you feel worse, will almost certainly make you more tired. Sometimes putting up with symptoms triggered by eating just has to be done in order to avoid the problems caused by not eating enough. Hopefully in time you will find a diet that minimises your symptoms, and treatment that will get your disease under control, but for now you need to do your best to give yourself adequate nutrition as well.