I was diagnosed pityriasis rosea two months ago, the dermatologist prescribed me to use betamethasone valerate, a steriodal anti-inflammatory. Some of the patches in my breast and abdomen are healed but the mother herald was not, and now I see some patches slowly up to my foot, arms and legs. Can pityriasis rosea last more than 2 to 3 months? How can I prevent it to stop spreading?