C.F.
My son is now almost 7 months, but like your son, always slept well...from 9-5, waking up to nurse, then back to sleep till almost 8 usually. That was between 1-5 mnths. Then at shortly after 5 mths old, he'd wake 3 or 4 times during the nite, i'd nurse him, and he'd go back to sleep....but this last for 4 weeks. Until we gave him some baby food...immediately he slept all nite again. He also started teething at 5 mths, but the teeth never seemed to bother him too much. The food helped him sleep. At least for 3 weeks, now he's back to waking once or twice, but I think we need to start food more than once a day....
I THINK if you try giving just a little food around dinner time (we did half a jar of vegetable to start) u might find this to help.