How To Get Relief From Sore Thumb After An Injury?

Hello. I'm Cindy and I'm 17 years old(5'6'' and 100 pounds). About three weeks ago, I was playing volleyball with my friends and the ball hit my thumb instead of my hand. It continued to hurt afterwards but I shrugged it off because I thought it was just sore. However, it continues to hurt a few weeks after. It hurts all the time but more severely when I jam it. What should I do? I haven't seen a doctor yet about this issue.