All of a sudden DS won't co-sleep?

My DS is almost 4 months old and we have been co-sleeping since day one.

About a month ago I started having trouble nursing him to sleep at the beginning of the night. So, we started putting him in his crib at the beginning of the night. At first he was waking up after two hours just as I was coming to bed so it worked out perfect. I would just bring him to bed and nurse the rest of the night.

Then he started sleeping longer and longer, which I didn't mind because I could get an hour or two of sleep without him in bed.

Then he started getting up between 3 and 4 and wouldn't nurse to sleep. So my husband would get up, swaddle him, rock him to sleep and place him in his crib, whick is at the foot of our bed. I know he is tired because my husband has him down in 15-20 minutes.

But now he doesn't want to stay in bed with me period. Last night after his first waking I took him into bed with me and it took about 30 minutes of popping on and off the breast and fussing before he finally fell asleep. Then he woke every 45 minutes until 1:30. By 2:15, he still wasn't sleeping so my husband got up and put him in his crib. Then when he woke up at 5, I tried bringing him in our bed and he wouldn't have it.

DS never really nursed to sleep during the day but I never had problems at night. My husband and I are finding it really difficult because we aren't used to actually getting up at night except to change a diaper. I have tried getting up at night with DS but for some reason it doesn't work with me so my husband has to do it every time and I am starting to feel really bad because he has to get up and go to work.

I am just really confused because DS is a very high needs, in arms baby. Six weeks ago I couldn't even put him down for a nap and now he seems to sleep so much better without me. In fact, this afternoon he was dead tired and so was I so went to bed and tired to nurse him to sleep for a nap. He would not sleep. So I got up and swaddled him and 30 seconds later his eyes were closed.

I enjoy co-sleeping and I especially like the convenience of it.

Has anyone else experienced this?