Jesus fucking Christ no! Don't skin pop ANY street drug, ever, but if there's possibly one thing that would be THE WORST THING to skin pop it's BLACK TAR!
Excuse my caps lock but I cannot emphasize this enough: you will – and possibly already have – irreparably damaged your body!
You say there are 'water' bubbles that have remained for a long time. What color is the skin that covers these 'water' bubbles? Because you may have covered yourself in abscesses! I would suggest.. demand even, that you go to see a doctor ASAP, no kidding, exaggeration, etc. I suggest a general practitioner unless your 'water' bubbles are black or otherwise discolored, in which case the ER might be best, but I hate to recommend the ER on such limited and vague information since there may be many people that will need the ER more urgently than you, and thus an extra patient can delay their care. But then again as I said we need to know your bubbles' color, because it may be that you also need urgent medical care.
So lets have some details, and please for the sake of your health and your life, unless dying from sepsis sounds like something fun to you STOP SHOOTING BLACK FUCKING TAR INTO ANYTHING BUT YOUR VEINS! Even your veins are not good to shoot that garbage into (note that I am a heroin addict as well and IV powder multiple times a day, which is also unhealthy, but tar is WAY more harmful still), but IM or subcutaneous is seriously a bad, potentially fatal thing to do.
So, STOP SKIN-POPPING TAR!