I have a (almost)5 month old lab mix. He already weights 42 pounds. He had his neuter surgery 5 days back. He was always slightly scared of the outside and hesitant to leave home (slightly climate controlled

). At the same time, he would never do his business inside. I started taking him to the dog park and spending more time with him outdoors to help him get over that slight fear. Since the neuter, he has reverted to not wanting to leave home. I go home at lunch to let him out to pee. He has stopped going out at lunch and controls it till I get home. Sometimes, he doesnt want to go even then! Last couple of days the holding time has hit about 12 hours.
Also, if someone comes over and he really is fond of them, he greets them and sprays them at the same time (only after neuter!).
When he eventually ventures out, he doesn't make it to the grass downstairs but pees on the stairs!
The only trip outside that he readily goes for and actually beats me to the door is the very first one early in the morning around 6:30 am. I understand its much quieter and much cooler at that time than the other times that I would like him to relieve himself!
He is on pain meds but i'm slowly tapering them off and tomorrow will be the last day.
He is eating and drinking water normally.
He has never woken me at night to use the bathroom.
Is it normal and healthy for him to control this long ? Will he counter a urinary infection due to this ? Is he just growing up ? I think he is physically slightly bigger than labs his age (42 pounds at 5 months).
Any guidance is appreciated! I am a new mother!
Thanks!