That sounds painful and scary.
Do you normally ever have pain and nausea as soon as you take a few bites? That has happened to me but not back pain and it was in the middle of a bad flare where just my body knowing food was in my mouth starts all the gastric juices and digestion and I’d have to run to the bathroom doubled over. The problem with Crohn’s and pain IMO is that they are so connected so one person’s pain might be intolerable to someone else (like who doesn’t have Crohn’s or colitis) I’d say if you are experiencing bad pain then go to the ER; they can at least run some tests and give you something for the pain. But also if it were me I might just do a bowel rest and not eat until Monday and the get to your GI dr. I had my stool change color to a light tan and after the rabbit hole of the internet was concerned it was my pancreas or kidneys. So maybe go to the ER if that’s a brand new thing too with the pain. Good luck! These things are awful on the weekends.