An air carrier flight crew deviated from the cleared arrival into LAX when a wake turbulence encounter and fatigue distracted them from the clearance.

Narrative

We were on the SEAVU arrival into LAX. We had experienced some wake turbulence on the arrival since we were following a larger aircraft. The autopilot was turned off during the wake turbulence and the First Officer was hand flying the aircraft. I was busy trying to re-engage the NAV mode since it was also disengaged for some reason. We were issued instructions to descend via the SEAVU arrival and cleared for the 25L approach (we both thought he said 25L). I was then trying to figure out what altitude to put in the altimeter. Once we were set up and tracking the 25L localizer we were switched over to a different approach controller. After we checked on with final approach we were asked by the Controller which localizer we were tracking. I responded with 25L. He said we were supposed to be on 24R. He gave us a heading and told us to intercept the 24R localizer and cleared us for the approach. We had no other problems with the flight after that. We had planned for 25L and were busy dealing with wake turbulence and automation when we were cleared for the approach. Fatigue was a factor as well since it was late at night. I had flown a redeye the night before and did not get much sleep during the day on my layover. LAX can be a tricky airport to fly into since they clear you to descend via the arrival and clear you for the approach at the same time. We were never told which runway to expect ahead of time and there was absolutely no emphasis on the runway we were cleared for. When the only communication is 'Cleared to descend via the SEAVU 2 arrival and cleared for the 25L arrival' it can get a little confusing and mistakes can be made especially if you're tired! I suggest asking LAX controllers to have better emphasis on what approach you are cleared for or tell you which approach to expect before issuing the clearance like they do elsewhere.