I just got a tadpole from the petstore and it seems very lethargic and sometime can't help flipping upside down What is wrong with it?

Some of the tadpoles I have were doing that and then a few days later they were fine. I think it is because they swallowed some air and it is in their digestive system. The tadpole should be fine in a couple of days. If the food you are feeding them floats, I would try to make it sink so there is a less chance of the tadpoles swallowing more air.