Well youre a female so it COULD be different but Im pretty sure youll be go to go on getting another script that day IF the doctor wanted to. I dont know how long youve been off it but some like to wait a few months before a second course.
Ive been on Bactim before and its probably the best antibiotic for acne. I would request that like you said but Im not so sure Id start Differin again. It'll just cause you to breakout more, making your situation worse, especially if you only use it for a month. Me personally I would use Bactrim and some sort of BP until you get on Accutane. Most topicals are going to take 3 months to start seeing results so less is probably best in your case. Give your skin a little break before you start Accutane.