My son is 6 1/2 months old right now, but he was never a good sleeper. We had SO many problems with him and it was so hard. He sleeps really well now. This is our experience.
I didn't believe in letting him cry it out, so I would go to him every time he cried. Up until a certain age, that is fine, but I think I did it too long and he became reliant on that. He seemed to only sleep in our arms, in the swing, or in the bouncer. He would wake up the second we tried to lie him in his crib. If we did get him to lie down, he would wake up ever 45 minutes throughout the night and NEVER nap! He was exhausted and so was I.
So I decided that my only option was to let him cry it out and it was very difficult, but I became so fed up with him being so demanding that I became a little hardened.
What we started doing was to have him lie next to us in our bed at nap time or at nighttime. We weren't going to bed, but we wanted him to know that it was okay to lie there and he was okay because we were right there kissing him and telling him it was okay. Of course he still screamed because he wanted to be rocked or carried around the house which was exhausting. So after he would cry for about 30 - 45 minutes with us lying next to him, I would pick him up and let him recover a little, but not let him fall asleep in my arms. Then lie him back down. Then I would eventually feed him (I'm breastfeeding) and he would fall asleep. I would let him lie in the bed for a while sleeping and then try to transfer him to his own bed and he would wake up, But I just kept him in his bed and let him cry because he was just asleep. He would cry for 30 minutes (I would go in and pat his back, kiss him and tell him it was okay about every 5 min which normally made his crying worse, but I wanted him to know that I was there). Then I would pick him up, but not let him sleep in my arms.
Eventually after a few hours, I would let him fall asleep in my arms and then lie him in his crib. Sometimes he would stay asleep for an hour or two and other times he would wake up right away and we would start all over. It was very tiring, but over time it has worked.
When he would wake up during the night, I would let him cry for a little bit, maybe 5-10 minutes and then go in and pat his back. Eventually he became satisfied with me just being there and rubbing his back that he would fall back to sleep. So he was taking the second best thing (he would prefer me to hold him, but he knew I wasn't going to). If it was time to eat, I would feed him (if it had been 4 -6 hrs). Now when he wakes up at night, I don't even have to go in there, I just let him cry for a few minutes and he goes back to sleep.
Now getting him to nap was harder because he would cry and cry in his crib because I think it was harder for him to fall asleep since it was light out. So that has been a process too. But we're getting there. He gets better every day. I think the main thing is being consistent because they are smart and know what they want.
Some babies don't do well with crying it out and I know my little one didn't do well when we first started it (I think he was a little too young), so this experience is from the second time we tried it when he was about 4 1/2 months old.
Well hopefully my experience can help you a little bit. I hope sleep comes soon for you. My son still really doesn't nap. Maybe once or twice a day for MAYBE 30 minutes. He's just not much of a napper and some kids are just that way.
let me know if you have any more questions. Sorry my explanation was so long!! Good luck.