This might be unrelated — have you tried investing in a shower filter? Depending on where you’re located, water can be over treated and very hard. I had pityriasis rosea recently for 5 weeks all over my torso, neck, chest, arms and upper thigh area. Within a few days of installing a shower filter, it noticeably cleared up. I’m really sorry you’re dealing with this. If you’re interested, I got it from here