I've had an annoying twitch in my right thumb for two days. Its not painful or showing any sign of weakness. Should I be concerned and see a dr?

No worries right now. No need to push panic buttons. Sometimes, a part of the body gets into a "twitchy mood" for no apparent reason & it goes on even for a couple of days as you describe but then, stops. Generally, nobody will be able to find a cause and life goes on. You may wish to avoid using that hand to hold grenade pins down and defer being the RACE TIMER for your kid's track meet until it stops. LOL.