How quickly should it work?
Pain usually improves within 24 to 48 hours, largely because of the steroid reducing the swelling. Full resolution takes the week.
No improvement at all after 48 hours is worth reporting rather than waiting out the course.
Why does it sting?
The acetic acid. It is unpleasant but expected, and it settles after the first couple of doses. Warming the bottle in your hand first helps, and prevents the dizziness that cold spray in the ear can cause.
Can I use it if my eardrum is perforated?
No — this is the one that matters. Neomycin reaching the middle ear can damage hearing permanently. If you have ever had a burst eardrum, have grommets, or had a sudden discharge that relieved severe pain, say so before using it.
Can I go swimming?
Not during treatment, and keep the ear dry. Water is what caused it in a great many cases. A shower cap or a smear of petroleum jelly on cotton wool keeps water out while washing.
Why has it come back?
Usually because the ear keeps getting wet, or because cotton buds are still being used. Cotton buds strip the protective wax and scratch the canal, which is precisely how infection gets in. Nothing smaller than your elbow goes in your ear — the advice is old and it is correct.
My ear is itchier than before. Is that normal?
No, and it is worth acting on. Increasing itch on treatment suggests either a neomycin allergy or a fungal overgrowth, and both need a different medicine rather than more of this one.