I hyperextended my knee and am experiencing moderate pain when walking. Is there a need to get it checked out or can I just expect it to be sore?

Sprain knee. You may have just sprained your knee. Use ice, a nsaid, and rest. If it does not improve after a week get it checked.
Yes if swollen. If the hyperextension injury was very painful, accompanied by a "pop" and/or there was alot of swelling within 24hrs then yes it needs to be checked out by pcp or ortho doc. Minor sprains or injuries have little swelling and see noted improvement within a week.