How can i tell if i have a broken thumb or torn ligament instead of a mild sprain of my thumb?

Several : Several things can be occuring 1. A trigger thumb where the tendon gets transiently locked causing the distal joint ( near the nail) to become stuck. 2. A swollen joint from being contused ( in this cases it sounds like the mp joint) causing the joint to glide less fluidly 3. An injured collateral ligament at the ulnar aspect of the mp joint 4. A small fracture at the joint level 1, 3, and 4 need treatment 2 might get better over the next day of two if it does not get better seek out medical attention.