Whenever I have a cystic acne, I always apply AHA+BHA and leave it for 15 minutes. Then I will use a cotton pad soaked with hydrating toner (make sure it's alcohol-free) to apply on top of cystic acne. It usually flattens down within 2-3 days. Make sure that you never squeeze the pimple as it will leaves a scar.
I have the same trouble! Always at THAT time! But since I’ve beem doing Cliniques 3 step mine haven’t been nearly as bad, or last as long! And when I do get the odd one/two I zap it with their Clinique clearing gel. Hope this helps x