Can You Get Fluid Buildup Behind Your Knee? I Was

Can you get fluid buildup behind your knee? I was training with weights to strengthen my Hamstrings and probably overtrained. I believe I strained the Hamstring but not sure. I can walk fine, but when I drive for long periods, I have alot of discomfort. I have been icing this for over 2 weeks along with stretching. The swelling behind the right knee has not gone done?