He also may be hitting a growth spurt and want a little more -
I would try offering both sides at a feed, if he is not wanting the second one wait maybe 15 minutes and try again - count as one feed.
Also, adding a little more time between feeds every couple days is a good way to stretch them out as well.
I know some people have been very successful at getting to the 3-4 hour EASY and nursing, but for us, we spent a long while at 2 1/2 hours apart during the day - he just wan't going longer! The biggest key for us at that point was sticking to the routine of not nursing to sleep instead of being so dependent on the clock. Hang in there - you are doing a great job!