Dog bladder infection?

My dog is four years old. We recently got him fixed in february because he wouldnt stop marking in the house. you could let him out 50 times a day and he'd still find something to pee on. So, after we got him fixed the marking in the house stopped completelty, not even one accident, until about 2 weeks ago. There was a bad thunder storm and hes terrified of them and i guess while he was laying on the bed he peed. Which even when he was marking he never did it on my bed. So i umed it was because of the storm. Then 3 days ago he peed right in the middle of the floor, and then last night he peep while walkin in the basement. this isnt his motto seeing as how he would hike up and mark on something before. Its almost like he couldnt stop it and was peein. He gets let out plenty of times during the day. About every 2 hours or so. (since he's a little papillion i figured he'd need to go out more) so, what i wanted to know is, could he possibly have a bladder infection, or could it be something else. he has a vet appt. wensday but i just wanted to know maybe what to expect. Thanks