Cguen

I wouldn't worry that much about the yellow stool because weird stool colors aren't uncommon the first month or so after surgery. Your insides have been mucked around with, so you're likely to see weird things until everything settles down again. I had yellow stool for the first month or so, too.
and the diarrhea part isn't unheard of. Yes constipation is a LOT more common, but some people have diarrhea instead.
the vomiting, stomach pains, and not being able to keep water down is a bit odd, though. I think I'd be tempted to go to urgent care or the ER this weekend if this keeps up - if nothing else, for peace of mind.

Did they do a CT scan? With the fast heart rate, they really should be checking you for a pulmonary embolism. Not being able to keep down water, with diarrhea and vomiting, it is definitely concerning and may point to a blockage or stricture.
I agree with @catwoman7, you might want to get back to the ER.
Of note, I had diarrhea the ENTIRE time I was on liquids - so I'm not surprised there. But, I only had vomiting for a day or two after surgery.

Have you tried calling your surgeon’s office? Even if they’re not open on the weekend, they probably have an on call service during off hours.

It sounds to me like you are severely dehydrated. Did they give you fluids in the hospital?
About two weeks after my surgery, I developed metabolic ketoacidosis, high heart rate and was admitted. They gave me what they called a banana bag of fluids and nutrients.
Severe dehydration can cause your high heart rate, vomiting, and diarrhea. Your high heart rate can also be atrial flutter brought on by dehydration. I had that, and the heart rate that is approximately double normal is a key symptom.
As Jeanniebug points out, you should also be checked for blood clots and a CT scan for leakage. I was checked for both while admitted.They thought they saw a small clot, and I was placed on blood thinners as a precaution.
Please get with your team ASAP and get this checked. Your team should have someone on call from their answering service. Mine did, and I was admitted on a Saturday. Be persistent. Consider the ER if required.
Lastly, don’t worry about stool color as you go through a rainbow until your system settles and you get into a normal routine.