For A Very Long Time Ive Had This Microscopic Little

For a very long time ive had this microscopic little bump on my inner left elbow, probably from when i had my blood taken when i was a kid. but randomly a few days ago it swelled up pretty big and is now like a knot. it probably only hurts because i keep messing with it but id still like to know what it is. im not worried just curious. it also had a little white dot at the center.