Hello~I would certainly see your GP about this, it may be nothing but then again, it could be something major, it is always best to be safe than sorry.
Here are some causes:
Diverticulitis
Celiac disease
Gas
Lactose intolerance
Inflammatory bowel diseases
Indigestion
Shingles
Irritable bowel syndrome (IBS)
Hernia
Constipation
Kidney stones
Intestinal obstruction
Here is a link to a site that might shed some light on your issue, but as I said, you do need to be checked by your GP and have some tests run.
https://www.medicalnewstoday.com/articles/320069