Kristi: Do you have a set time that you expect your ds to go to bed or do you try to get him to sleep when it's obvious that he's tired? My ds went through some changes around a year old. He was going to bed much later than before primarily (I think) because he was still taking 2 naps a day, with his afternoon nap sometimes lasting until 5 or 6pm, which would push back his bedtime.
I ask you about a bedtime because if you are expecting him to go to sleep at some predetermined time, this could be where the trouble is. However, if you do try to get him to sleep when he's obviously tired and he's not acting like he used to then I'd suggest mixing things up a bit. Try some new approaches. Can you put a mattress or bed on the floor in your room or in his room?
My ds is 2 and we've slept all over the house. Now, though, he goes to sleep in his room (nursed to sleep or bounced on an exercise ball) and sleeps on a mattress on the floor. If he wakes up before I go to bed, which he usually does, then I tend to him again, either nursing or bouncing back to sleep. Then, when I'm ready to go to bed, I sleep in his room with him. Dh sleeps in our king sized bed by himself! This arrangement has worked the best for everyone and we all get plenty of sleep. We've been using the mattress on the floor in ds's room since he was 9mo. Prior to that, ds slept with me and dh in our bed.
Good luck...I know how this can be...just when you think you've got some stability, they up and change it! Keeps life interesting, huh?