E.J.
My 2nd daughter was on zantac until she was about a year old.
It didn't bother her going to the bathroom or other tummy issues.
Are you breast feeding her? They sometimes don't make any bowel movements that often and it might be something you ate that is making her tummy ache. I know onions or garlic and sometimes if I drank milk it would bother my 2nd daughter.
I know you can give her myclin drops for the gas.
One thing I did learn about the zantac is that it will stain clothes. I went out and bought the big bibs so that if she spit up after taking it it won't get on more of her clothes and ruin them. My daughter is now 3 yr old and health but we do not let her overeat because she will spit up on occasion.
Hope your daughter feels better soon!