Question about Pepcid AC. Please help

Hello,

 I took Joy to the vet and he prescriped Pepcid AC. She's been on it for 24 hours now and her appetite has gone from eating less to eating nothing and hiding. Her urinalysis and blood panel is normal. Doc will now recommend an ultrasound. Just going to the vet is 100 times more stressful for her. Stress may cause it? We have two other cats and two dogs. All was well until I had to switch her off dry food last Feb and after trying a ton of good healthly food finally found one they all at, but the last month she's been eating less and lost a pound or two and now weighs either 9.2 (my scale) or 9.10 vets scale. I have been hand feeding her when I notice she doesn't eat much. I do think she is on the lighter side myself. When she ate dry food she was huge, prob close to 11 pounds. 

I just don't know what to do and am thinking of stopping the pepcid to see if she goes back to at least eating a little. 

So that's the background, my question is I take liquid vit b12 myself. I wonder instead of a shot I could just put some in her food? I wonder how much to give??? Anyone know? And would it be safe?

Thank you!

Karen

Oh, and I forgot to mentions, all other behavior is normal. Fun, frisky, playful, alert, loving. She does't act sick.

Thanks!

@kitschcat,  please don't stop giving the Pepcid, until you check with your vet. Also, the B12 needs to be discussed at the same time. B12 is a powerful vitamin, could cause severe harm.

I am not a veteranarian, and advise you to take your vet's advice. Please contact them before doing anything else.

Okay, I am speaking with him in the morning.
Thanks

I don't think the Pepcid caused further decrease in appetite, it's probably what ever the original cause is.  Pepcid usually only works if excess stomach acid is present.  If there isn't an issue with excess stomach acid then it won't help but I don't think it will make things worse.  Before my IBD kitty was finally diagnosed I tried Pepcid and it didn't help him.