How Can Recurrent Ear Infections In A Toddler Be Treated?

My 2.5 yr old kid had an ear infection in right ear few weeks back which was treated by the use of Candibiotic ear drops (5 days, 3 times a day). After one week of no infection, he has again got the ear infection in the same ear recently. He is not in pain, neither itches his ear and does not have a fever. At the start of this infection we noticed that he had a dark brown discharge during the morning sticking at his ear hole once (photo attached). Took him to pediatric doctor and based on prescription, he is on Candibiotic ear drops (2 times a day) and sodium bicarbonate-glycerin ear drops (3 times a day)since last 7 days. His ear gets fine till the time we give him medicines but as soon as we stopped candibiotic yesterday, we can see brown crust forming inside & on edge of his ear hole today. Seems like the infection is still not treated. How long do we have to continue with ear drops? Also can you suggest any better treatment & medicines/ear drops for the same.