The problem that you are facing is a common one,,,and is seen in many patients who are prescribed Isotretinoin
,,,,and it is called retinoid dermatitis
...But first of all, i would like to assure you that it is nothing to be worried about,,,,Your doctor must have assessed your skin condition and prescribed isotretinoin according to the severity of your problem,,,,so you can continue with the medicine without any doubt,,,
The problem usually begins after some days of treatment with dryness which is followed by some fine scaling. In the more severely affected patients, the scaling gets worse and fissuring develops and this is what is occuring in your case....Dryness is seen in most of the patients who are prescribed isotretinoin,,,and it is very beneficial for acne prone skin,,,infact, it is one of the mechanisms by which the drug acts....
So all that you need to do is to moisturize your skin,,,Use some Oil free moisturisers or you can apply little bit oil over skin once a day...But remember not to over moisturise,,,,For your lips, use adequate moisturisation in the form of lip balms, petroleum jelly....and use a sunscreen before going out in sun over your face regularly as any type of eczema
leads to irritation on exposure to sunlight...
If inspite of all these measures,,you feel that the irritation is increasing or is persistent..,then you should consult your dermatologist
Hope it helps
Dr Geetika Paul