The reason why it comes back once you stop the ointment application is that once you stop applying, the suppressive component is lifted and your immune system begins to act awkwardly again. Topical steroids are known to cause skin thinning and its one of their side effects. Steroids are also prescribed for wounds to heal without scars ( they delay wound healing, so prevent scar formation). Its better not to apply them over open wounds as it might be absorbed more into the body system. You cannot completely say that the stretch marks were caused by steroid use, while they do cause skin thinning, its not going to cause that much big stretch marks. I advise you to get yourself reevaluated by your dermatologist, and , maybe I feel its time to change your medicine.