What Is Meant By Lymph Vessel Block & Is It Serious?

My 4 year old son had a swelling in hisleft foot on the top. We treated him for an insect bit. Now the next day there was awatery fluid coming out of it and the swelling has not reduced. Doctor has prescribed anti biotics and says that if it does not subsire, it could be Lymph Vessel block. What does that mean and is it very serious condition?