The problem is fluid retention because the drugs are causing you to be sensitive to salt and so salt is holding excess water in your body. If you cut down on salt you will excrete some of this water and therefore lose weight.
See http://www.wildeaboutsteroids.co.uk/steroids.html and other pages on the website.
Lose weight, reduce your risk of most cancers, high blood pressure, type 2 diabetes, stroke, heart disease, vascular dementia, osteopenia, osteoporosis, hypercholesterolaemia, depression, liver and kidney problems, and improve your health in many other ways without drugs or expense by eating less salt! - Try it! - You will feel so much better!