Hello @agoodmind4u -- welcome to Mayo Clinic Connect. I'm sorry you haven't been able to find an answer to the facial swelling yet but it sounds like you to have identified the probable cause. Others have mentioned the FODMAP or low FODMAP diet for IBS. While we wait for other members to respond to your post, I did find some information on Mayo Clinic's website that may be helpful.

The role of lifestyle-related treatments for IBS
-- https://www.mayoclinic.org/medical-professionals/digestive-diseases/news/the-role-of-lifestyle-related-treatments-for-ibs/mac-20431272

You mentioned eating very little and changing sleeping positions. Have you made any changes to the types of foods you eat?