Pink eye (conjunctivitis)?

I took my 5 y.o. to the Dr. on Monday because of a lot of purulent drainage from the right eye. He gave us prescription for eye drops. On Wednesday the pink eye spread to the left eye so we started in with the drops on the left eye. It's Friday now and I'm just wondering why he's still waking up with his eyes crusted shut. How long does it take for the antibiotic eye drops to start working?