I would try moving the second bottle back a bit. Your lo is going 4 hours between the first bottle and then 7 hours between the next two. I know it is more important to drink milk rather than solids at this stage, but one of the girls on this site posted a routine for me which really helped with his eating and when i should be giving those 3 bottles. It looked something like this:
a typical routine with 3 bottles looks something like this:
7am bottle
8am solids
10am Sleep
11.30am wake
12noon solids
1pm bottle
2.30pm sleep
4pm wake
7pm bottle & bed
Of course, ive tweeked it a little to suit my ds and you can do the same. Maybe if you give a bigger gap between the first and second bottle, lo would drink more. It may take a couple of days to settle into it though
Also, like i said, it could be teeth or developmental issues, and eventually your lo will sort it out. I was worried too about ds's low intake but a couple of weeks later he is now having between 6 and 8 oz at each feed
HTH