What Causes A Movable Lump Near My Knuckle Causing Discomfort After Blood Was Drawn From My Left Hand?

Hi there, about 10 days ago I had my bloods drawn from the back of my left hand. The doc punctured my vein, the one near my middle finger and told me it s perfectly fine and the swelling will go away. Sure enough it subsided the next day. But I masturbated and a couple of days ago used said hand and felt a slight pain come from the knuckle. I have since not been able to switch to that hand. I noticed that when I press w (keyboard gamer) I feel slight discomfort. And there is a pellet sized ball at the side of the knuckle which is noticeable when stretching out finger. Moves as it s finger becomes outstretched. Even feeling slight discomfort holding my phone as I type this.