Yellowish green mucus in eye. Issue?

My daughter is 4 months old. From last few days her left eye remains watery all the time and some yellowish green mucus use to come from it. I use to clean her eyes with sterilized cotton ball three times a day. Here pediatrician prescribed her 1 eye drop namely "Ap drops" 3 times a day for 7 days. After using that it got cleared for 2 days but again it started. Corner of that eye become reddish due to the watery discharge. The pediatrician now is adv ising to contact an eye specialist. Here to mention that she got the same problem when she was 20 days old. That time Tobacin was used along with tear duct block excercise. Now I am very much worried. why is this happening so frequently. Is this only for blockage of tear duct or for some other issue? Please guide me she is too small. Please help