It's good news that he's not had any vomiting or diarrhea yet, but that may well be right around the corner for him if we can't get his upset stomach straightened out. That's part of why you're hearing the loud bowel sounds and he's been eating weeds.
There are a few things that can be done at home to help make a pet with a stomach upset feel better. 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 you do not see an improvement from the famotidine and offering a bland diet, I would recommend going to your vet's office for an exam and anti-nausea medication to be administered injectably to help get his GI tract feeling better so that he's not avoiding his normal food and eating weeds. Your vet may also want to run some blood work due to his age to be sure there are no underlying concerns that need to be addressed, like dehydration or organ dysfunction. Most pets do quite well with symptomatic GI treatments and are back to themselves within a few days time.
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