Steroid Injection for Cyst

Hello
A month ago I broke out with about 5 cysts on the right side of my chin. I have since had them injected and am on Minocycline 200 mgs (2 weeks so far) for 3 months along with Differin gel. Otherwise I have pretty good skin, the monthly pimple or 2 but that is it. I have been very stressed though for the past 6 months.
I have one cyst in particular injected 2 times now (smaller from first injection), yesterday being the most recent, yet it is still raised. How long does a cortisone injection continue to work? Has it done all it can within 24 hrs or does the shot continue to "melt" the cyst over a couple of days? Will I need to get more? Or should I just wait for the Minocycline to kick in?
Thank you for time and thoughts,
SS