At 8 months I would expect most babies to be having 3 bottles in the day and then some still have a dreamed or nightfeed. Have you tried putting another bottle in just before the afternoon nap? That's the most common pattern really with 3 bottles, a wake up feed, post lunch/pre nap and a bedtime feed.
You may find that weaning the night bottle helps the day time intake too, particularly the first feed of the day. I would start reducing that by 1oz every 3 nights so you wean it slowly.
The other thing is to scale back solids a bit, especially the tea time solids, until milk picks up a bit and then gradually increase solids again. It's quite common to need to do this, of course it depends on how much he is eating.
Laura