Mama, I really think you should check with your pediatrician about this, they'll know the best timing for your baby's confirmatory test at 4 months old, especially since it's such an important result to confirm.
A few of us mums had similar concerns with newborn screening, and honestly, ang doctors talaga ang best person to advise on when to re-test para sa G6PD. Don't worry, you're doing the right thing by following up on it now! Kelan ba siya nag-test first? Your pedia will guide you on what's needed next.