I Am Unable To Bend My Thumb Without Pain. It

I am unable to bend my thumb without pain. It catches and hurts just below the fingernail bed. I can do it manually but not on it's own due to a lot of pain. Although at times I can, but the pain returns. I worked as an apple packer. They worked us at a very rapid pace. I am thinking it may be the cause. I have seen others asking this question and their answers have been flexor tendon injury. Is that likely what this is?