Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice.
In a diabetic with an infection, the foremost step in infection control is control of sugars. The sugars need to be really well controlled because if sugars are high, the infection cannot be controlled and what is more , it can recur easily.
The second part is taking the antibiotic. You will need to take it very regularly. And usually, if the sugars are not well controlled, antibiotic course will need to be prolonged so as to be effective.
Last and most important, meet your dentist
before stopping the antibiotic for any possible visual inspection of the site for possible confirmation regarding the infection control. If it persists, the antibiotics will need to be taken longer, preferably without stopping/interrupting the course.
I hope this helps. Feel free to clarify on any point as deemed fit.