If the symptoms are not completely abated; you need to go to out of hours surgery, so further course of antibiotic can be continued without interruption and there is no gap so bacteria would not develop resistance to the antibiotic. The reason of inadequate response can be;
1) The bacteria which is causing present infection are either less sensitive or not sensitive to the amoxicillin.
2) The infection severity is high so it will take longer course of the antibiotics.
You can also do following also;
1) Increased uptake of water and fluids; 2.5 to 3 liter per day.
2) Avoid caffeine and alcohol drinks
3) Drinking Cranberry juice.
Please feel free for your follow up questions.