Hi Suzie. Welcome to HealthcareMagic. It is difficult to say anything unless it is seen and evaluated. If you had been injected some medicines in that place it might be that due to some micro trauma there had been some oozing of blood and a small haematoma
had formed. Since you have mentioned that you have stents implanted it is possible that you are on antiplatelets and this might have caused bleeding at the injection or injury
site. Please show it to a doctor asap.