Pretty sure Rey is Luke's daughter.
You have to figure, after the events of "Jedi", there wasn't much left for Luke to do. The Empire had been overthrown, all the other Jedi were dead. Luke probably went on an intergalactic tour as I'm sure there were billions of people/creatures that wanted to get a glimpse of the man who saved the galaxy.
Can you imagine the endless waves of Jedi-groupie trim that were being thrown at him? The guy would have had to have been neck deep in poon of all species 24/7/365. Eventually, it wore him down and he just said #### it and started dropping his cargo like he'd just seen the first sign of an Imperial starship. 3 ways, 4 ways, Eiffel Towers, all while Ben, Anakin, and Yoda watched and ghost-whacked off.
Eventually and predictably, the women he bedded, emboldened by the absence of Imperial tyranny, began filing child support suits looking for their share of the Skywalker fortune. Facing a lifetime of legal imbroglios, Luke fled to the first Jedi temple where he could Force choke his chicken in solitude. That map was being sought not only by Kylo Ren but by legions of women raising illegitimate Skywalkers who were tired of their kids waving their little hands and saying things like "You will give me another cookie now..."
The look on Luke's face at the end of "The Force Awakens" was born of the abject horror that accompanied the realization that one of his horde of ******* progeny had finally tracked him down. My guess is that episode VIII will begin with him taking his old lightsaber back from Rey, immediately chopping her in half with it, then escaping to some even more remote location in the Outer Rim where he can recede into a cave and lope his mule in peace until the sweet release of death finally comes.