My 8 yr old had appendectomy 4 weeks ago till now he still passes gaz and complains of stomach pain and very busy bowel movement is this normal moreov?

Possibly. Children receive strong broad spectrum antibiotics at the time of surgery and for a period afterwards if the appendix is ruptured. These antibiotics can predispose to c. Difficile infection which could cause your child's symptoms. Get a stool culture.
Probably. Pediatric patients vary on recovery rates; however, most take 6-8 weeks before life seems normal again. Besides the intestinal aggravation of appendicitis, there is the muscular/abdominal wall tenderness triggered by the surgery itself. Due to the symptoms affiliated with appendicitis, your son may not be eating his routine diet. Avoid carbonated drinks & cruciferous veggies. Probiotics may help.