There is always a bit of post injection redness and swelling which may or may not itch. You might be mistaking this for a "rash". It should subside on it's own in the next few weeks. If it does not or the symptoms get worse then you will need to be examined in person by your injector.
Are you sure that what you have is a rash and not just the typical post injection redness and swelling? You will be able to see and feel little raised "bumps" where the filler was injected. These will resolve in time. If your "rash" doesn't improve within two weeks, see your surgeon. Best of luck.
