There are quite a few things that this could be linked to. Since he is 11 weeks old, we always concern ourselves with parvo, distemper and intestinal parasites even if the puppy has been vaccinated and dewormed. Additionally, any dog that is eating mulch can easily acquire a major GI upset from this.
Because he is so young and he's been vomiting so often, I would recommend that you visit the ER hospital this weekend to get some diagnostics started and anti-nausea medication started so that he does not further dehydrate. With dogs this small and this young, it doesn't take much to push them to a critical point where hospitalization is required. The hospital will likely start with a parvo test and a fecal exam to check for intestinal parasites. As well, they may recommend blood work. SQ fluids may be recommended along with a shot for nausea like cerenia.
If you are unable to do this, I have posted directions below on trying to stop the vomiting and a bland diet, which sounds similar to what you're already making for him. If the symptoms persist, he absolutely needs to be seen Monday.
The first thing is to administer a dose of regular pepcid (famotidine) every 12-24 hours. You will want to give 0.5mg/pound of body weight (a 10# ***** would receive 5mg, a 5# ***** would receive 2.5mg, etc). For this, you can buy the brand name Pepcid, or you can use the cheaper, off-brand “famotidine” that’s available. Either will be useful.
2 hours following a dose of famotidine, the time needed for the medication to begin working, you can offer a bland diet. To make this, you’ll combine white or brown rice, boneless, skinless chicken breast and sufficient water for cooking in a stock pot. Boil on medium until it turns to mush and the breast is easily flaked. To avoid more nausea, start with small amounts to begin with and offer the amount every 2-4 hours. A few teaspoons to start is typically sufficient and you can work your way up every 2-4 hours in incremental increases until you’re sure no vomiting will be seen.
If your companion requires a more palatable food, try adding in pureed baby food in chicken, turkey and similar flavors.
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