Baby not getting enough?

Breastfeeding has been so hard for me mentally, I feel like I’m always overthinking and questioning if she’s getting enough. My baby is 4.5 months & was in the 24th percentile at her 4 month check up. My pediatrician wasn’t concerned and suggested just topping her off with an ounce or two of breast milk/ formula after her last two feedings of the day. She is so so fussy at the breast & just doesn’t always seem satisfied. She was born with a lip and tongue tie but we’ve had them revised. I’ve met with 3 different lactation consultants. It’s just hard to know if it’s because she’s not getting enough, or if it’s because she’s just impatient waiting for a letdown, teething, tired, gassy, etc. it seems like there’s so many reasons why she could be grumpy, but how do I know if it’s a supply/ transfer issue or not? She’s still peeing & pooping. I’m about ready to just throw in the towel, I feel like it’s frustrating for both of us. but I’m worried if I switch to EP I won’t produce enough, and if I switch to formula it’ll be hard on her tummy :( I just want her to be happy & healthy & when she is grumpy I can’t help but feel like it’s a feeding issue.