Hi, So A Couple Of Weeks Ago I Injected Heroin

Hi, so a couple of weeks ago I injected heroin into my arm I.e. IV, and i ended up missing. And this morning i woke up and it hurt badly to bend my arm open and closed.. I rubbed it and felt a harder lump under my skin. I was going to go to the doctors today, but my health insurance company just recently moved out of the area so i currently am waiting on getting new insurance. I'm worried because the pain is getting bad(hurt to raise my arm up and wash my hair in the shower this morning). I plan on going into an opiate rehab once my insurance kicks back up.. But I'm clueless as to what to do right now. Theres no mark on the surface at all, his a harder lump a little bit smaller than a bouncy ball under my skin. Any information would be greatly appreciated.... Thank you for your help.