In three days? That's fluid not fat.
You should have your doctor order some simple blood tests to determine whether you have hypothyroidism or not. The tests you need are Free T3, Free T4 and TSH. You might also ask for thyroid antibody tests to determin if you have Hashimto's Thyroiditis.
Prednisone is a steriod and, typically, causes weight gain, rather than weight loss.