WOW! That's a lot of formula

But he does weigh almost 20 lbs and most babies will drink 2 - 2.5 ozs per pound of weight

So really, he is right on course!
A good option for encouraging solids is to offer them before a bottle feed when he is most hungry... don't push it though

What are you trying to feed him? I found that DD was actually most receptive to a bit of banana mashed with a fork with a bit of formula in it for moisture (and it makes the taste a little more familiar). A couple other popular ones with babies are carrots and yams... steam some carrots and whiz them in the blender until smooth... use formula for moisture or water (just not the cooking water - nitrates from carrots). Yams can be steamed or baked then blended as well... same thing, add formula or water for moisture. Babies have a natural sweet tooth

All of these are low on the allergy risk scale as well

I would try to avoid a small bottle before a nap - it could lead to a feed-to-sleep problem
