Stretch marks are pretty much impossible to get rid of all together, but they do fade over time and there are some creams you can use to attempt to sped up that process. Some suggestions that I have heard is vitamin E oil, Mederma for stretch marks, and products with Shea butter in them.
These typically are suggested for stretch marks that occur naturally (like in pregnancy), so you may want to check with your doctor since you started seeing the issue when using a steroid.