from personal experience its a build up of oil,test prop is notorious for that and if painful its because it crashes in the muscle and slowly disperses. I have injected test prop in the bicep,calves and lower quad right next to knee and learnt the hard way as all spots got hard,warm,painful,lumpy and red and within the week disapeared.So if its gone in a weeks time it aint no abscess but just your luck,try pumping 2ml in your ventro glute as it can take up to 5ml with ease and rotate with glutes. hey even till this day when I inject test prop in pecs and delts I get a warm painful lump and goes away within 2-3 days,damn prop!!!