Blood in stool. I go for colonoscopy?

My 2.5 years son having blood in stool past three months. Three months ago he got high fever and diarrhea and blood in stool. He gave pacimol mf, taxim o forty, probiotic and zanocin 150.In April he got little loose motion and blood in stool for two days. He gave super flora gg drop and bleeding stop. From 7 th may he getting blood in stool again 2-4 drops after 3-4 days interval. Doctor stop all milk and wheat products. But no improvement . Stool report, usg report, urine test all are normal. Obt test also negative. We are sure it was blood. Now I have done a stool culture test and get E. Coli in culture. The blood is bright red in colour, sometimes see on toilet paper. My question is the blood due to E. Coli? Or it due to anal fissure or juvenile polyp? Should I go for colonoscopy?