I am Dr Mbong.
Each vial of long acting forms of cortisone
can last for weeks to months (1-3) in the blood system.
So with the 13 injections it can take 3-6 months before their effects wane from your body. This will depend on how good your kidneys are, how much of water you drink (to make your kidneys eliminate the better) and on your diet (rich in fruits and vegetables and low is fat, cholesterol
Doing some physicial exercise (I know your joints hurt but try and do so with a professional's help) in a gym will also help you loose weight faster and get your kidneys and sweat glands get the steroids
out of your system, faster.
Wish you well,