Thank you for your post-- as a parent, I can certainly see why you would be frustrated-- it is your right to know what is going on with your daughter and I'm honestly baffled by a father who refuses to take his daughter in for treatment and diagnosis.
My first thought when I read your subject title was Roseola-- since it's very common in infants and toddlers and both of my kids have had this. However, Roseola presents itself in fever form first and then once it's gone the rash breaks out and there is no antibiotic prescribed for it.
My next guess is that it's either Scarlet Fever or a strain of Strep Throat.
These are treated with an antibiotic and, unfortunately, the side effects of the antibiotic may be causing stomach pain and diarrhea. If the pain and diarrhea are severe and she still has a long ways to go with the medication, it is probably best to call her doctor. If she's almost done with it, she can finish it but I'd give her a probiotic, which can be purchased at a drug store, for her tummy. As a matter of fact, I'd give her the probiotic regardless of whether or not she was almost done.
Is her fever getting better? 101.5 without medication is not ideal but not terrible either. It's probably even best that you don't bombard her little body with Motrin/Tylenol on top of the antibiotic if it isn't necessary. So, if they are limiting this to once a night and it isn't going over 101.5 then she will be okay.
I can only speculate on what it can be, it may be another bacterial infection but seeing as she has been put on antibiotics, then she is getting treatment. Try to be positive. It seems that the bigger issue here is the lack of communication between her father and you.
Wishing you the best,