From your description, when you said he gets 3-4 times solid meals, what does he eat? I am thinking he is probably too full from the solids that he does not want the milk. Or he simply has no more interest in milk. You can supplement the nutrients of milk through other dairy products like cheese, yogurt, fresh milk. If you really want him to take milk you can reduce the amount of food he eats, since you say he is overweight.
Is he not sleeping well & crying at night because he is not feeling well? My girl will also cry for my attention if she is not not feeling well because obviously, she can't sleep well with a cough, or blocked nose.
Does he cry non-stop at bedtime or he falls asleep, then wakes up crying non-stop? If he cries at bedtime he may be too tired already. If he wakes up in the middle of the night crying it may be due to night terrors, which is quite normal.
What does nap time have to do with whether your boy is overweight or not? Naptime helps them to rest & recover some energy for the later part of the day. As for the sleep part, according to Baby Center toddlers at this age need about 11-12 hours of sleep at night & take 1.5-3 hour nap in the afternoon. Is your boy getting enough sleep? Cause if he sleeps at 11pm and wakes up at 8pm I doubt so.
You are definitely not alone on this. dont't think about dying just because your boy is tough to handle. Every mummy has her own challenges & if all of us here want to die because our babies are difficult to handle, then there'll be a lot of orphans around. Stay strong for your baby boy.