Lomotil is a drug that can be used to treat diarrhea, but is contra indicated in patients that are dehydrated. Do not administer anything without talking to your vet, as dosing is pretty specific for cats. Lomotil is light sensitive, so it requires careful handling. The side effects include hypotension, aggression, constipation and seizures so this drug should be monitored very closely by your veterinarian.
IBD is an illness that cycles, and stress can cause flare ups. Some cats vomit, some cats have diarrhea, some cats have both. I have an IBD kitty, and there are times when it is hard to manage his symptoms. Those times usually correspond to times of stress and excitement in my own life, and my cat is responding to me.
It sounds like you and your vet are on a good path to managing your kitty's IBD, but check out the following website for some more information. It may be helpful to you.
Discuss your options with your vet, and I hope your kitty feels better soon. Let me know if I can be of further assistance. If this has been helpful, please hit the green accept button. Good luck.