Sore joints and fingers and thumb, could it be a tendon thing?

Possibly but rather. Improbable, as there is no single tendon going to all fingers or the thumb. Sounds more lie some arthritis, gout or pseudogout, unless a crush injury to the whole hand has affected multiple fingers/thumb. Do get yourself checked by an orthopod or a hand surgeon. Your pcp can help direct you in the right way. Good luck.