PIO knot/lump following shot

Hi ladies,

I’ve been doing PIO shots for awhile, and for the first time, I’ve developed a hard lump/rock underneath the skin, immediately after the shot. I called my clinic, and they informed me that this happens sometimes, and to use the other side - but I’m wondering for those of you that have experienced it, how long it took to go away and if anything helped? I tried slight heat and massage...