How is pitch controlled in a flying wing?
You basically have the answer right inside of the question (as was mentioned in the comments).  In order to make the plane pitch up and down you have the ailerons move up or down in unison (usually called an elevon at that point, again, as noted in comments.)

Here's a handy diagram to give you some idea of what we're on about:



In the second image the movement of both elevons upwards will pitch the aircraft up as well.  And the elevons going in opposite directions, like the last image, will cause the plane to roll (in this case to the left.)

There are more complex maneuvers as well, like pitching and rolling at the same time. These maneuvers are simply managed by differential deflections of the elevons.  Meaning, if you want to come up and to the left you could leave the right elevon neutral(ish) and pitch the left elevon upwards.  This would push down the left wing, rolling you to the left, and pitch the nose up as well.