House Trained Dog Keeps Randomly Weeing?

My 14 month old Yorkie Poo is toilet trained. But the other day, after he sat by the open door all day, I carried him to the next room and he did a wee down me. We thought maybe he hadn't gone out because it was rainy and I had pressed on his bladder. But then 2 days later, after he had been out and about all day he was sat on my bed next to the open door and he peed all over my pillow. It was sprayed everywhere like he cocked his leg. Nothing has changed lately and his brother hasn't had any problems.

By Amy