My Havanese is 13 weeks old. I am very careful to keep her away from areas that might be exposed to illnesses and such until after her last set of shots. She is normally very energetic, crashes, and repeat all day. Yesterday, she was lazy and slept or just sat around most of the day. She didn’t eat very much. She still went potty regularly. Last night, she had some diarrhea. Today, she did eat like she was starved, but she is still laying around. She does get up and move around, but she doesn’t really want to play.
I did give her a new kind of treat a couple days ago. It was the same brand as her dog food. I won’t give it to her anymore. I’m wondering if it could be teething or something? She will gnaw on the bully stick for at least 30 minutes at a time. She does appear to be in any pain. She is just not as energetic as she normally is. No diarrhea today. Any advice?

Sounds exactly like my puppy. He would play and wear himself out, sleep and repeat. Take advantage of it! I used to do our little training sessions and play time right before I needed to work on something because then he’d just sleep.

My Hav has a sensitive stomach and often gets diarrhea from packaged treats. I have learned if I’m trying something new to only break off a tiny piece and I don’t give it on an empty stomach. I think protein source has more to do with sensitivity than brand. Also, a lot of them list the daily portion (say 2-3 treats per day) yet don’t specify what size dog that applies to. When I’ve tried to find out online or by calculating on my own I’ve often learned that my dog can really only have 1/2 of one. I hoard packaged treats that don’t smell because it’s handy to have something non perishable on hand that doesn’t stink, but I try to rotate in small bits of table food as treats, too. Mostly fruits and vegetables (he LOVES snap peas) and small bits of unseasoned meat from meals. A probiotic helps us, too. Any change in food in the beginning can cause diarrhea, but there’s been some research posted in the threads here and elsewhere that suggests slowly introducing and rotating foods and protein sources can help prevent problems, provided there aren’t any food allergies. If I was doing it again, I’d rotate proteins each time it was time for new food. No pressure! Don’t let the over abundance of information and advice on diet overwhelm you, this is just coming from someone with a Hav with a sensitive stomach.

If you suspect he’s sick, don’t feel like you’re overreacting to take him to the vet. Even if he does have all of his shots, giardia is rampant this time of year in my area, which has a lot of snow the freezes and melts again. I know it also took time for me to be able to read my puppy well in those kinds of situations, so it was better to be safe than sorry.

I can't offer advice. Willow has had diarrhea in the past which was caused by poultry. She has lazy days where she'll sleep a lot but it's the diarrhea that you mentioned that would be a little concerning. If it continues I would see the vet. Please let us know how she does.