Hi C.,
I echo what Sara F. says - great book! And he is probably ready to give up the third nap.
My daughter was on a 4 hour routine at about this age, too. She gave up the 3rd nap somewhere between 6-8 months - it was on/off for a little bit. Our routine (for sleep and nursing) was something like this:
7 AM - wake/nurse
9AM - 11AM (ish) - morning nap
11AM - wake/nurse
1 PM-3 - afternoon nap
3PM - wake/nurse
6:45 - 7ish - bedtime routine, nurse, then down for the night
She slept through the night at this age. We were gradually adding solids into her diet starting at 7 months. We added them one meal at a time, I'd nurse first and then feed food. Eventually she was eating solids at her 3 daytime "meals", and as we weaned after her first b-day, the meals stretched out in time a bit to become breakfast, lunch, and dinner.
So a couple thoughts...it sounds like he needs more breastmilk or formula. At this age, b-milk/formula is baby's primary source of nutrition. Food is more about baby learning to chew and swallow and give some nutrients. Maybe offering breastmilk a couple more times during the day would make it so you wouldn't have to wake him to eat at 9:30. Also, if he wakes up at 6AM, he might need to go to bed earlier, maybe more like 6:30 or 7:00 (I know that's hard in lighter summertime days!).
Just some ideas - hope it gets figured out! Could be teething, too. You're definitely on the right track!