Go back to the dentist asap, it could be a dry socket!!!!! Antibiotics are great but they won't help with a dry socket. A dry socket is simply when a tooth is pulled a blood clot forms, if the clot falls out too soon a dry socket can occur and then the site becomes extremely painful! Hope this helps.
If it's a dry socket, they will usually pack the site with Eugenol, a clove based medication. The packing is changed over the next several days and usually the socket will heal and the pain goes away.
If amoxicicillin does not clear up infection in 3 days, you may request your dentist to switch to other antibiotics, such as erythromycin, clindamycin, or cephalosporine.