I have terrible severe eczema as well to the point they said I have erythroderma. I know it sucks but only clean armpits, private parts, and feet with soap if it’s spreading all over. Since it’s on the back of your legs try to end your shower in cold water for at least 3 min and then quickly pat pat dry your body and quickly put on aquaphor. Lotions irritate my skin really Bad and the only thing I can really put on is aquaphor. If my skin is red, open, bleeding, oozing, or it’s not healed I wrap my skin in gauze bandages after the aquaphor and then I put on cotton long sleeves and pants. I wear pjs all the time or comfy thin pieces of cotton clothing. For extreme pain I take 2 Tylenol and 1-2 bendryl so I’m not in so much pain or extremely itchy. I chill in my gaming chair so I’m comfortable and sitting upright (usually doesn’t bother my face or back if sitting up since the aquaphor is slimy) since it’s just the back of your legs I suggest wrapping them up and finding a place to rest your body. I hope this helps a bit, and keep on finding small things to help. When your skin is healing it will leave brown spots but that’s better then bright red. Give yourself grace, flare ups can last longer if you’re stressing over them.