I always leave mine in at the dentist. They just say you know that could damage your teeth etc etc. And that is all.

There will be a small mark in your tongue where the hole is if you do take it out. And if its out to long it will be sore after you put it back in.

Leave it in.

Yes its normal to hurt mine was fine after about 5 days. Just make sure your cleaning it like you should. If you think some thing is wrong call the place you got it pierced.