Vienna, I used to have this problem all the time, along with going many times a day,(sometimes 20+), and feeling like I couldn't get everything out when I did go. Miserable! After some research I decided to get a food intolerance test called an ELISA, which is meant to identify foods to which the body has a delayed allergic reaction, (Igg). After eliminating the problem foods a lot of those IBS like symptoms disappeared-but then I was dx with crohns.
My symptoms improved so much after eliminating the Igg foods that I would have been satisfied and not gone on to see a GI, but the GP found a mass in my lower right and suggested a CT scan.
It could be possible that you are experiencing IBS along with the crohns. I have also had success with the Low Fodmap Diet which I found out about
here on HW, (thanks to the person who posted about
that!). Sadly, crohns keeps giving us new challenges--I hope you will be able to figure this one out and will be feeling better soon!