Help! Puppy bowel habits completely changed

[kingkuta]

Pup is 16 week old zuchon. From about 11 weeks he's slept through the night without waking for toilet and goes straight out in the morning then once afternoon & evening. However for the last few days this has completely changed. Wees as normal but no poos at all during the day then up once or twice every night. So first poo early evening, another late evening then up at least once in early hours maybe twice. I'm shattered! Poos in early hours are a lot softer than normal as well. Not sure how I can get him back on track to daytime poos. I've tried moving evening meal back earlier but doesn't seem to make a difference. Also moved him over to Butternut food a couple of weeks ago so not sure if this is causing it. Anyone got any advice?

Go right back to routine and food when he was fine

How slowly did you switch his food? Is Butternut box even appropriate for such a young puppy?

As a young dog that's likely not from the most reputable breeder, he needs testing for giardia

The food was switched over a week as per the advice from butternut and their food is tailored for puppies as well as older dogs. He was fine on the butternut for the first 3 weeks then this started. He's teething quite badly so I'm wondering if this can affect it?
I'm going to give my vet a ring this morning and see what their advice is. Thanks all