Frustrated with Breast Feeding!

Having a frustrating day. My baby girl is 1 week 4 days. My first baby had a terrible time breast feeding due to being early and having a tongue tie. I did everything to help him latch, including feeding with formula via tube on my nipple for 6 weeks, pumping after each feed to increase supply and having his tongue tie cut, twice. I could never get enough milk to EBF. My daughter started off as a dream breastfeeding. Latched right away and no tongue tie. She was a big baby at 9lbs 8oz and went down to 8lbs 10oz. She has not been gaining weight fast enough (currently 8lbs 13oz) and we have been topping up with formula. I just can’t seem to get enough milk and now her latch is becoming very narrow and painful for me. I had such high hopes breastfeeding would work this time I’m feeling a bit down. I have no problem with formula, but I like the convenience of breast feeding. Putting all of the extra effort into boosting my milk supply is harder this time because I have another child to look after. I want to breast feed (whatever I can) for as long as I can but am feeling so defeated today.