You're not a failure, you're just still finding your way and figuring things out. That's what parenting is all about, so you're doing well (it just doesn't feel like it most of the time)
Have you seen an LC, or called the ABA? You definately need real-life, in-person help with getting breastfeeding right sometimes.

For mastitis the best thing is to get your baby to the breast to clear it. But if you've cracked nipples then that suggests your baby's attachment is not quite right. An LC can probably help you with that.

Take care of yourself and all the best