I Have Taken My 6 Month Old Shepherd In For

I have taken my 6 month old shepherd in for lethargy several times she now has a huge gland on the one side of her neck it has become so large I am afraid it will soon obstruct her airway The vet said it had red blood cells and bacteria. It has become larger since taking the antibiotics we were given this time. I am very worried what could cause one side swelling