You probably are not processing fats as well as you did before the surgery, hopefully for just the short-term. I know that's a tough pill to swallow, but you may have to very, very slowly introduce fatty foods back into your diet and see what happens.
Unfortunately, no one really knows whether or not it will change. Some people can happily eat fatty foods again, while others are unable to.
It still might be to soon to eat fat like that. I have the same problem, still have my gallbladder and I would get very sick if I ate that. There is something they can give you to help process the fat. Ask your doctor. I can't remember if it helps with diarreah or constipation after cholecystectomy.
I know it sucks,
Everybody is different. I had my gall bladder taken out February 27. My biggest fear was digestive issues post surgery. Everything has been going pretty much as the doctors said it would. In the past week I've eaten pizza, Indian food, Thai food, Ice cream. And today I had Mexican food. I took it easy the first week, crackers, oatmeal, stayed real bland and low fat, but I am just about eating normal now. No real problems so far (knock on wood).
If you think that you may still be having problems with fat, try taking bile salt tablets with anything that is higher in fat. I actually have been taking these for a couple of months now, before and after surgery.