inside of elbow on left arm hurting any ideas on whats going on

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4 days ago i woke up and it is really hurting right in the joint of my left arm in the bend right behind my elbow. the day before i didnt lift anything or do anything to hurt it. i went to bed fine and the next day i noticed it was sore and tender. then everyday since it has gotten worse. now it hurts to straighten my arm out to the point i dont do it often. if you feel in the bend of my arm you can feel like a knot or its swollen etc. it doesnt have any bruises or anything though. it is kind of like when you get an IV and its in your arm for about 24 hours and they take it out just with no marks. anyone have any idea of what is going on and what i should do. i have iced it, done stretches, etc