Trouble with frequent ear infections

I have a Boston who has had frequent ear infections since the age of 7 mns. She will be 2 in April. It mostly effects one ear at a time and usually is the left ear. It seems like once a month we are having to take her to the doc. They give her MalOtic and this will clear it up, but it just returns. The doc. said she might have food allergies. Could this cause ear infections? We have switched her to Purina One, chicken and rice, trying to limit to one source of protein. Sometimes she will not have an infection, but swelling of her penna in the ear. It usually gets very swollen and red and hot. The MalOtic will work on this also, but it always returns. She seems to have a lot of foul, dark, almost bloody drainage from the infected ear and I do clean her ears when I see signs of the dark wax. She will scratch and scratch, sometimes making the ear bleed. I am just not sure what to do for her... It seems like we are taking her to the Vet every month for the same problem. I know it has to be uncomfortable for her and I just hate it. Any help or advice?