How long until amoxicillin works for an ear infection?

I got a spontanious ear infection tonight. I get them all the time and always get prescribed amoxicillin. Unfortunately, all the clinics were closed tonight so I was just going to wait but then it started hurting so bad I couldn't help but take some of the amoxicillin from a previous ear infection!! How long until the pain will become bearable?! I know it's bad of me ot use old stuff but I had no choice, it hurts so bad! Unfortunately i don't know how old the bottle is..