Thank you for the query.
Blood and mucus in the stool is usually caused by large intestine disease including inflammatory bowel disease
, large intestine polyps or even colon cancer
. This conditions should be ruled out at first.
Food poisoning would give rather nausea and diarrhea than only mucus and blood.
Right upper abdominal pain
especially when radiates to the back, is caused by gallstones or sometimes by pancreas disease.
It is advisable for you to have some diagnostics. Abdominal ultrasound, full blood work, liver tests, amylase, bilirubin and urine analysis should be performed as well as colonoscopy
Hope this will help.