It would be wise to really baby the foot now and try to make the effect last as long as you can. Unfortunately, I have had experience with cortisone and it only gives a short-term temporary relief -not a cure.(this has also mentioned by other people on this site)
Also, you it is a medical reality, that a person can only have so many shots of that stuff, especially to one particular body part... and each time you do have one you run the risk of "blowing" your facia or losing your fat pad on your heel... at least these two consequences have been described previously by several people on this web site. All things considered, caution and a long discussion with you doctor before more shot(s) would be wise.