On day 9 of bad cold, and day 3 of 875 mg of amox. for ear infection after flying with said cold. today snot turned canary yellow. normal? also have a sinus dip over retained babytooth- can that complicate congestion?

Sinus infection?: If the nasal discharge becomes more yellowish as late as the 9th day of a cold, one needs to suspect the presence of sinusitis. In most cases, the amoxicillin would have started working by now and thus check with your doctor to find out if a change in antibiotic may be needed. In the meanwhile, try saline irrigation on the sinuses.

Continue antibiotic: Sounds like more than a typical cold - possible sinusitis or other bacterial infection with the ear infection. For now I would continue the antibiotic as prescribed and follow up with your doctor if not better by the 7th day. Make sure to get plenty of fluids and rest. Vitamin C is also helpful. Good luck.