Hi there,
I hear you!! Our little one will turn 13 months in less than a week and she's just under 18 lbs! My husband and I are both very petite so that partly explains it. Having said that, she's SUPER active and doesn't eat a lot. She does know how to use a sippy cup but she isn't a big drinker, either, so getting her to have a nice cup of milk before bed, doesn't work. She has never, ever slept through the night and like your son, saved his eating for during the night. Hence, I'm a very tired mama! I decided 2 weeks ago that whether he's truly hungry, or just waking out of comfort, is irrelevant. The habit needs to be broken so I can get some sleep.
Our little girl is very strong-willed so there have been no miracle transformations on our end in terms of getting her to sleep through the night in 2 or 3 days like so many of my mommy friends were able to do with their babies. What I've done so far, is put her to bed (usually between 6 and 7...depends if she skipped an afternoon nap), and I don't nurse her at all unless 6 hours has passed. That means if she wakes up at 9, 10, 11, etc, I go in and pat her back and walk out. No eye contact, no singing, no talking, no picking up. I just lean over, pat her back for about two minutes and leave. There are times I have to repeat that scenario 3 or 4 times before she's asleep. I know many people would say I should just continue to do that all night long but once 6 hours has passed, she's usually pretty hysterical if not nursed, and the patting/walking out, just doesn't work. So, despite my desire to sort of go cold turkey, I've had to be more flexible than I had otherwise planned.
Good luck...I know it's hard.
-R.