What Causes Swelling In My Feet Followed By Dark Skin At The Site?

i have a small small swollen (i am not sure whether they are lymphnodes or not) but when it swell it is very painful. but after few days the pain is gone but the swell leaves there and become a bit dark. and there it goes day by days. my feet are full of dark circle caused from the swollen. i need to get a blood check in a few more days. but now, can u pls explain to me, am i infected of something dangerous ? pls answer.