I agree with everyone mentioning to have your dog checked by your veterinarian to start with.
If all is well, it may be behavioral - if he likes to go outside and by waking you up, he gets to go out, he may have developed the habit.
It would be important to know whether he CAN "hold it" all night without going outside. If he CAN'T - there is likely an underlying medical problem. If he CAN but he just wakes you up, he may be waking you up to go outside, not necessarily because he has to pee.
If there is no medical problem, you may have to start gradually "ignoring" or "delaying" letting him out so that he will break the habit.
It's similar to feeding a pet whenever they beg - pretty soon, they learn that begging gets food.
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