Allergies and breastfeeding

Amber

My baby tested negative for allergies on a stool test that checks for blood; however, she is fussy and gassy. She doesn’t poop unless I give her miralax or suppository, and her poop is VERY mucousy but not green. She acts like she’s in pain when she passes gas and she spits up more than she used to. Could the test be wrong? Should I take her to a gastroenterologist? Just want my baby to feel better.