After you beat Diagla, you will unlock Luminous Spring, but you wont be able to evolve your starters. So, in some time you will get a dream about Cresselia leading to spacial Rift and Dark crater. Just follow the story...
Hope I helped!
A bit after Manaphy joins you it should stay in Chimecho's Assembly post not in your room if you did than Manaphy should have showed you a new area a couple of days later or on the day you recruit it it is called Marine Resort.Later the two Ursaring say something is different at the Luminous Spring than you should evolve.(depending on the pokemon)