Suggest Treatment For Black And Red Bruise On Leg

2 days ago I experienced a stinging sensation on my right leg just below my knee.At first I thought I had been biten by a mosquito,on closer inspection I saw a vein large and swollen protruding from the skin instant throbing and itching took place.The swelling took about an hour to subside,and have been left with a very large black and red bruise.Its a little tender and I notice when I am on my feet it tends to throb.Hope you can help