I woke up today with a sharp pain in my left thumb. last night it was fine. no sign of bruising or injury. what can it be? it moves ok but its painful

Thumb pain: Consider sprain, contusion, tendonitis, or neuritis. Try ice, purified omega, rest, activity modification tip better.

Could be anything: There are strains which can occur to ligaments which aren't felt at the time of activity but cause pain later. Certain arthritis conditions can show without any outward signs but pain and even some more uncommon things that could do this. Use common sense. Rest the digit and use otc anti-inflammatory medicines. If not better in a couple of weeks or if things are worsening, see your doctor.