Help on if this could be cancer or what?

i have a swollen lymph node on my right groin went to doctor and got ultrasound done and it is 4.5 cm my whole leg is very sore including the lymph node it is tender to the touch..it has been there for little over a week it just all popped up at once and then the pain started the next day..no other symptoms but i do know that a lymph node 4.5 cms is very big and cant be good..help me if u can in finding out lil bit about what it could be