My baby has never been a good sleeper. He usually wakes about 3am and seems starving hungry. We are still having to buy formula so we can feed him during the night to make him go back to sleep again. I've tried leaving him to cry but he could go for hours! Help!
Your baby associates falling asleep with sucking on a bootle of formula, He is waking out of habit and as you are rewarding this behaviour by feeding him he will carry on. You can offer him water when he wakes, he won't like this at first but if you persist he will learn that the milk has stopped. Ensure that he is going to sleep on is own and not falling asleep on the bottle.
At 13 months you can give baby whole cows milk. What time do you give him his last bottle at night? I only give my daughter a bottle now occasionally (23 months) when she asks for it but I literally just stopped it all together. Like Kate says, changing it for water or simply stopping it all together might just solve the problem. Maybe also have a look at what you are feeding him during the day at at what times?
It's such a horrible situation but the above answers are both right. Your baby has learnt that when he wakes he can feed in a cuddle until he falls asleep. Firstly switch to water, which agreed he will hate, but he will soon learn it's all he can have. Then I would recommend that you do leave him to cry. I have been a controlled crying parent and although hard when they go on and on, just go back in occassionally to settle them so they don't feel alone, other than that it's best he begins to learn to settle himself-as hard as it is to hear!