My ds started with some night wakings at the same age. I don't know if it was developmental, some seperation anxiety, night terrors, or what. What helped us get throught them were offering water when he woke, as sometimes he was just thirsty. Keep the talking and interaction to a minimum, so as not to encourage it. Has he gotten his molars and eyeteeth yet? If not these could be the culprit and some pain meds before bed may help as well. We also dealt with early wakings as well. When ds woke really early I would go in to him and pick him up if need be, and he would cry and scream to go downstairs, and for milk, etc.. But i would just tell him no and that it was time to go to sleep. He would carry on and I just stood firm that we were not leaving his room. Eventually he would be ok to go back in his crib, and sometimes he would go back to sleep, and other times we would start all over again un til it was 6 and then I would bring him down.
Hope this helps and if you have any questions let me know!