Amoxicillin is an antibiotic not a pain killer...the pain will subside when the infection starts to heal if that is all you are taking for it.
If you need pain relief the start by taking ibuprofen, if that doesn't work well, then something like co-codamol would be more effective. For instant relief from severe pain Orajel's 'Maximum Strength Toothache Pain Relief Gel' works instantly and can be bought at most pharmacies.