I don't think 2.5 mg will cause weight gain or moon face on you. It's a very low dose. Just watch your snacking and drink plenty of water.
Since you have lupus of the skin (discoid lupus?), you need to be careful of the sun, fluorescent lights, tanning beds, and halogen lights. Make sure to cover up with sun protective clothes and some nice hats.
Lupus, Fibromyalgia, Glaucoma, Asthma, Hypothyriodism, Sleep Apnea, Degenerative Disk and Facet Disease, and Allergies
When life throws you lemons....
Pick them up and throw them right back at them! :))