Why can't he always sleep like this?

So here I am, it's 2:00 a.m.  I've been sitting here for 20 minutes waiting for Isaiah to fall back asleep.  He isn't crying in his crib, just talking to himself.  Just 2 weeks ago he started sleeping from 9:00 p.m. until 3:00 a.m.  He did this pretty much for the last 2 weeks and I was starting to get used to it!  Now all of a sudden he has decided to revert back to waking up around midnight/1:00 a.m. again.  (I think he may actually be asleep now!  It's awfully quiet on the monitor.)  Anyway, it's really rough because I've started back to work.  Before I went back to work, it wasn't a big deal.  I got to sleep in a little bit if I was up all night and sometimes I could squeeze in  a short nap.  Not now... See, it's 2:00 a.m. and in just 3 short hours I have to get up to get ready for work.  Plus he will probably wake up now around 4:00 a.m. to possibly eat again.  Even if Tim feeds him, it will still wake me up.  I'm glad this week is only a two day week for me at work.  I'm not sure if I could function through a whole week.  It's no wonder I'm falling asleep on the couch at 7:00 p.m. every night.  I need that nap to even make it through the night without going completely insane!