Antibiotics won't work if it's a sterile abscess.
What were you doing having scar tissue in the first place? And in the second place, what were you doing injecting into scar tissue??
After each shot, you should massage the hell out of it so scar tissue doesn't develop. Also, the oil gets injected VERY slowly, with the smallest needle possible for that reason.
If you do develop scar tissue, do not inject in that area until the scar tissue dissapears. You make it dissapear by deep tissue massage - painful!
That's my lecture.
Now, you have to stop all the shots in the area. Drain the abscess with a needle. After it's all drained, massage the hell out of the area all the time so the scar tissue breakes down. It will dissapear in time. The time frame depends on how much scar tissue you have there.