My 4 year old son has a middle ear infection, has being taking augmentin for the last 3 days. but his ear is constantly discharging yellow thick fluid. is this normal or should it have stopped by now?

Maybe not: Unless the kid has grommets and is draining the infection through them this would be evidence for a ruptured ear drum. With either the discharge would continue for a time pass when the germs were all dead. If the volume of discharge does not lessen over the next day or 2 I would have him re-checked in a few days rather tan a few weeks.

Not unusual. : Discharge from ear during an infection means eardrum ruptured and infected fluid, trapped in the middle ear is draining out. Recommend you keep ear dry; no dunking head in water while bathing or swimming. For best outcomes and relief, seek care from pediatric ear specialist (ENT/ otolaryngologist) to clean out ear canal and visualize eardrum. Continue Augmentin till full course is completed

Culture: If no improvement after 48 hours, I like to get a culture of the fluid in the office. It is not uncommon for MRSA to grow and a change in antibiotics.

Not unusual: Drainage usually stops by 5-6 days. If it continues beyond that, see your child's PCP. Sometimes ear drops are needed or a different antibiotic.