It is not holding an everstone, and the game has never been hacked or pirated or anything like that. Is it a glitch?
Right, this question gets asked a lot. Here is probably what's wrong:
Yes there is something wrong with your game. Swablu is suppose to evolve on level 35 and does not require any special conditions to evolve. Try catching a new Swablu and see if that one will evolve. If not you will either need to start a new game(Not sure if this one will work.) or buy a new copy to evolve a Swablu.