Mystery digestion pain that goes away when I lay down??

Hiya, I’ve had this reoccurring pain since I was a kid, I’ve had multiple tests done with no answers so hoping someone may help here!

-It usually happens after dinner/evening time. - The pain grows in area and level of ouch the longer I continue standing. -It doesn’t seem to be linked to any foods (tried all elimination diets) - It may be linked to anxiety somehow (I find I tend to get it often on nights out) - The only way to relieve the pain is by lying down. The pain disappears immediately, but will return as soon as I stand up. It takes 1.5-4 hours of laying down to get rid of it! - Always causes major bloating and usually gas, occasionally diarrhea.