Hi Mam,
Is the pain radiating from shoulder to hand? If so it could be cervical issues. But any ways as you have mentioned pain in thumb area it could be a possible dequerian disease inflammation of the tendon near anatomical snuff box. Kindly consult near by physician or write back with the pic of pain area and type of pain. So you can find a better solution.
Next Steps
Initially check your movements of neck and shoulder if you can move them freely this is purely a problem as mentioned above else should require a investigation. Also lump you have mentioned can be a lypoma or a nodule pl check it is a movable one or tender. If tender apply some ice initially followed by therapy for both.