Pulling back on the needle to check for air bubbles a white discharge fills the syringe. could this be a sterial abscess? no symptoms , just sore leg.

Depends on med: It depends on the substance / medicine in the syringe. Does it do this after you inject yourself or stick the needle in the vial? Are you injecting a hormone or other "milky-looking" medication? Or is it a clear medicine like insulin? And is your leg swollen? (from lymphedema?) I would direct you to your primary doctor or a qualified nurse and show them your technique and show them what comes back

More info: What are you using a needle on your leg (or whatever you're pulling back on) for? Although I definitely need more information to give you the best advice, I would advise that any time you pull back on a needle from somewhere on/in your body and you get a white return, I can't help but think it's a sign of infection. You may want to give your doctor a call.