Okay - we need a little more help from you, K.. When you say he cries all the time, are you talking all day or all night? Or both?
If anyone told you to let him cry all alone during the day, they are wrong. If you are talking about sleep training, there is a way to do it and definitely a way NOT to do it. If you are talking about night time, then you are doing it wrong.
I wish I knew which you mean. I'll start with day time. Surely you would have talked to your doctor if he is crying all day long. What did the doctor say? How does he eat? Is he gaining weight? Does he have a lot of wet diapers? How are his poops? Do you breastfeed or bottle feed? Does he tolerate regular food?
This is important to know. Babies cry when their tummies hurt. They can't tell you what is wrong. You have to figure it out. Start a diary. Write down what time he gets up and if he cries. What time he has breakfast (food?) and bottle. What you feed him and when he cries (before? after the food?) Does he have gas? Are you burping him enough? Write down about his diapers - when and what they are like. Does he take naps? Are you getting him up at the same time every day and putting him down for nap the same time every day? Is he going to bed at night at the same time? You should have the same routine for him with meals and sleeping/waking every day.
Does he cry when you hold him versus you putting him down? When does he NOT cry? These are things you must figure out so that you can explain to the doctor. Otherwise, the doctor is stabbing in the dark at trying to figure out an answer.
If he cries when you don't hold him and he can't stop crying, I would get a sling of some sort and wear him. I know that's hard, but if he is not able to break this constant crying jag, this is what you need to do. That way you can get something done with your hands. When it's time for him to take a nap, put him in his crib and sit beside the crib with your hand through the slats touching his leg. Sit on the floor so that he'll lay down to be closer to you. Don't sit in a chair because he will stand up and scream for you to take him out of the crib. You don't want to take him out of the crib. He must understand that sleep takes place in the crib. Always. Hopefully he will fall asleep soon. Don't let him sleep longer than a certain amount of time so as not to mess up his next nap or night sleep.
When you can, sit in the floor with him and your 2 year old and let him play on your lap. When he's comfortable that you aren't going to leave him in a room by himself, you might be able to do something in the room without him crying after you, but that might take a while.
For night time, I would recommend that you put a chair in the middle of the room, with a nightlight on, and sit in the chair after you put him in the crib. Don't look at him. Don't talk to him. Don't engage at all. If he cries, he cries. But he KNOWS you are there. He will get tired of the crying and fall asleep. Then you go out of the room. If he wakes in the middle of the night, do the same thing.
This is a different form of night training. You are very uninteresting at this point. You aren't picking him up or talking to him. You are NOT feeding him. You aren't fussing over him. Yet you are there in his presence.
I do believe in the Ferber method which I did with my kids. However, I think that you have been very inconsistent with your son and that he has issues that you have not figured out and because of these two things, I would not leave him in his room to cry. At all, K..
It might take a while, but if you are 100% consistent, it will get better unless he has a medical condition that causes him to be in a great deal of pain.
If he is crying all day, you need to get to your ped with this diary I'm talking about. He needs to have some tests run and your doctor needs to help you figure out what ails him. He's too old to have colic, unless this is an unusual case. I want to say that it's reflux, but you haven't said anything about his eating. Anyway, Good luck and keep us posted, okay?
Dawn