I am on phentermine diet pills. My dentist has prescribed me amoxicillin for an infection. Can I still take the phentermine with it?

Yes & no. There is not a specific drug interaction but if you don't eat or drink enough because of the Phentermine it can increase the negative reactions from the amoxicillin. I would recommend taking some form of pro-biotic such as acidopolous or cultural with your medications and plenty of water.