Hi hun, welcome to BW, hope we can help.
From what you say, sounds like you weren't with DS for these 2.5 months? In that case, I would say that this separation was a huge experience for him, and something it will take him time to work through. Given he's only 18 mos, he can't talk it over with you, so a lot of what he needs to 'say' will have to come out in his behaviour. If he's doing something awkward, it might be because he's worried, or upset. You will need to offer lots of reassurance that you will be staying with him. So to start with, I would offer lots of cuddles and tell him directly 'I'm here with you, I will stay' and that sort of thing, because they can understand more than they can say. Building his confidence now will boost his independence in the future.
I think what you're talking about here is a lack of routine, rather than discipline as such. As regards getting back into a routine with him, just reintroduce him to it - get him up around the same time every day, have meals around the same time, aim for naps and bed around the same time. If you are consistent for a few weeks, he will fall in with it. It probably won't happen overnight though. Serving meals regularly may help him to eat more during the day, and hopefully help out with those night wakings. We have an Eating for Toddlers board which you may find useful to read, or post on. Several mamas there with picky eater experience.
Eating For ToddlersFor helping him go back into his crib, I would recommend Gradual Withdrawal as there's a clear emotional element here. You need to be prepared to take lots (and lots) of tiny steps to get him where you feel he should be. Is he in his own room, or do you share a room with him? If he's in his own room, be prepared to camp out there with him for a few nights. Let him play in the crib during the day, with you in the room with him, let him see it's a fun and safe place to be. Don't push him to go in there, as it is likely he will just resist more if pushed! Do not try to rush him, you will have to be very patient, and willing to celebrate the smallest successes. I think the main thing for you to focus on is communicating to him that you're not going anywhere, that you are staying with him. So if, for example, he is in his crib and upset, you could sit on the floor rather than stand, so he can *see* that you are not leaving. As he relaxes into going into his crib, you will spend less time keeping him company, and will move away from the crib and out of the room more quickly. But it will take time.
Toddlers: Walk In/Walk Out vs. The Gradual Withdrawal Method (HOW TO CHOOSE) You might find this link useful - it has a section on crib phobia at the end - you will need to adjust it slightly for his age.
Regaining Trust of Your ChildHope some of that helps.