What is wrong with my weenie dog? help!?

he is a 4 year old mini dachshund i recently felt the outside of his mouth on the left side it feels like a thooth and then mintues later its gone.. and now its back again..thing though he is wagging his tail, eating fine and i see no blood he lets me go near his mouth i dont know what it is..i cannot take him to the vet until this friday but until then do you think you know what it could be >? Im worried thank you-Jess