Do you think he is getting enough food during the day? Is it possible that you have started a new food that is bothering him? Did he just go through a growth spurt and now he just has a habit of getting up.
You did not mention if he puts himself back to sleep. If so, that is great, and you are well on your way to his learning to settle himself down.
Is he getting too much sleep during the day? (Don't get me wrong, I think the more sleep the better, but I have found that too much day sleep affected my son's night sleep, although for him it was more in an earlier wake-up),
Could baby to hot/cold? Could there be a noise that is arousing him? (Our sleeps in our bedroom and i became really aware of how darn noisy the satellite TV receiver was, the disk drive spins up at 4 am, and in general the box is whirring on a regular basis)
Maybe he is about to hit a milestone and his little bring is waking him up with the excitement of figuring things out!
I think you will find his sleep will go back to the old pattern, even if you can't determine what is bothering him.
I will tell you that my ped said don't let our baby cry it out until 6 mos. The reasoning behind this had to do with his not being able to self-soothe until he was older.
If you are having to soother him, you may want to avoid putting him in bad with you (although, most of us have done it for the sake of sleep, so don;t beat yourself up). Some people theorize that if baby figures out he will get to share the bed, he will purposefully wake up for just that.
I'm sure you are tired. I hope you both get more sleep soon.