Wow...sounds extremely uncomfortable. It is possible it's a stress reaction, but with you having so much going on, and this happening again...i suggest you ask your doctor to request a biopsy of your lip.
How long did it last?
Re B vitamins...worth trying. What dosage? I would also add L-Lysine.
I found this...
https://dermnetnz.org/topics/oral-manifestations-of-inflammatory-bowel-diseaseq