Hi,
Thank you for the questions. In general, most people do see improvement within 1 to 3 months of isotretinoin treatment. The response does depend on the initial severity, dose of treatment and individual factors. In some individuals, there may be an initial outbreak before it gets better.
You are on 40mg of isotretinon which is a fairly high dose.
This can cause a lot of dryness of the lips and face. Using products containing benzoyl peroxide can certainly cause the skin to be more irritated and dry. I think it is best to stop applying this if you are experiencing skin dryness and tightness. It is good to continue with moisturizers to calm the irritation.
You should let your doctor know your concerns. Sometime, additional treatments like antibiotics may be prescibed if there is a bad flare to help settle it.
In majority of cases, the acne flares will settle while on isotretinoin treatment and the acne will be well controlled. I have seen really bad cases settle beautifully, so hang in there.