If you know anything about this, please help! My 2 week old puppy (St. Bernard) has constipation, he hasn't defecated for three days. He's still breastfed, and his mother eats dry food, milk, and tea sometimes. The puppy weighs 2,8 kilos. Please advise anything, I am really worried!
Give him something too eat to lubricate his intestines, which may work. Such as give some olive oils into the food.

I think you should change his mother's food since the puppy gets nutrition from her. I don't give the dog dry food. I cooked rice with some meats, some vagetables for her. Everymorning she has sweet potatos (though I don't think you have sweet potatos) which are very good for her digestion. Acid milk is also good for dogs.

Considering your puppy is still so little, I think you'd better go get some advices from the vet. They are professional.

Good luckEmotion: smile
Does the puppy look nervous in any way? If he had a real health problem, he most probably would behave anxiously, would be crying and his belly would be swollen. If there are no such signs, don't worry too much, everythig should be fine.
Does his mother lick his tummy regularly, by the way? If yes, then again - no reason to worry. If no, you have to massage it yourself after the puppy has eaten.

If you still think something is wrong, you can follow Dinosaur's advice and give him some oil - 1 mL must be enough. And yes, I'd reconsider the mother's menu. Give her puppy food only while she breastfeeds.