Pain under breastbone and nausea

I visted the ER a few weeks ago with extreme pain directly under my breast bone and nausea. An ultrasound was performed and I was told that my duct was very enlarged and it looked as though I may have passed a gall stone and had sludge in my gall bladder. I was still in school and was hesitant to get it removed because it presents another set of issues (diarrhea on eating fat) so I cleaned up my diet and did well for a while. I did eat a few things that weren't so good for me and started having nausea but no significant pain. Now my concern is whether this may be an ulcer and not gall bladder. Is it likely that this could be a gall bladder issue and still cause nausea, even without eating fatty foods? Might this be related to the pancreas? Do you have any reliable information on how long it takes the body to adjust to eating fat after the gall bladder is removed, are there just some people that never adjust?
thank you for your help.
angles mommy