I gave myself a b-12 shot about 2 months ago & just today noticed a hard painful bump, in the same spot (outside of my bicep). doesn't seem normal??

Scaring: Any type of injection can cause some tissue damage due to pressure and inflammation. Acute edema from injection may take period of time to settle down and then lump/scar may be palpable. Should decrease and settle down over time. Best not to give yourself an injection but allow medical professional to due it properly.

It is not: A shot 2 months ago would not usually cause a lump to occur. The lump may be something else. Possibly a sebaceous cyst or a lipoma (benign growth). Have the Dr. Look at it if time and/or warm compresses do not resolve it.