I have had a really painful, rough start to breastfeeding. So I took a break and pumped because the ulcers were torture and just pumped for a few days and fed my baby expressed milk and formula.
Anyway my nipples are mostly healed and I've gotten some great advice on latch. It still hurts, but less.
BUT I don't have nearly enough milk. My baby is so frustrated and my breasts feel soft. So I've been topping him up. He's a huge baby, too, and very hungry.
Can I do anything to get my supply back? Or have I ruined it? 
I don't mind mixed feeding, especially to give me a break at night, but it doesn't feel mixed, it feels drips of breast milk and mostly formula.