I breastfeed and formula feed -- 8 week old, is this normal?

Ever since my baby was a week old I've done both. Mainly because she wasnt gaining weight that first week so I started expressing milk and I would only get about 7ml! So I started using formula to supplement. We started out with half an ounce after feedings, but she wasn't satisfied, so we increased to about an 1 oz of formula after breastfeeding. Shes 8 weeks now, and I'm still doing the same. My supply is super low (I was never able to increase it, but I still try my best to breastfeed). Recently, shes been a lot hungrier, I nurse on demand and a lot of the times she is not satisfied with just breastmilk so I still give that ounce of formula afterwards. However, she's been asking for food more often, and not matter how often she nurses my supply won't increase, so I feed her just formula If feedings were close together. So keep in mind shes 8 weeks, even if I just feed her formula, she wont drink more than 2 oz. Is that normal??? It's not super often than I just give her just formula for a feeding. But no matter what she wont take more than 2, and shes pretty satisfied because she'll nap just fine afterwards.