Thank you for the query.
Bright red stool is most likely caused by blood in stool
which can appear due to hemorrhoids, anal fissure, inflammatory bowels disease, rectal polyps or even colon cancer. Lower abdominal pain
can be caused by diverticulitis
(mostly left abdominal pain), large intestine polyps or cancer, inflammatory bowels disease. As the pain appears periodically, partial bowels obstruction is possible.
I suggest you to do not wait anymore and visit your doctor. Physical examination should be performed, blood work, urine analysis, abdominal X-ray
and ultrasound. The next step should be colonoscopy.
Hope this will help.