Babies do indeed self-wean. At 6 months, my son stopped completely. He's been on formula ever since (started solids at 4 months), and he's doing well. (He's almost a year.)
Nursing is not easy on the body, especially if you're working. So I'd say that you've done enough. Furthermore, you sound miserable, especially since you've been suffering from mastitis, which can really make you ill if it's not treated.
And although La Leche is often recommended, they did tell my working friend that she had to quit her job in order to nurse successfully. So it's not everyone's cup of tea.
Start your baby on formula. (I'm sure I'll be flamed here for suggesting that. Both of my children were on formula for much of their first year and I've seen no dramatic differences between them and their peers. They are healthy and growing well!)
You've got to find a balance at this point. And if you have frozen breast milk, use it. But begin by slowly introducing formula, too, so that he gets used to it. And you really only have a very short time left before he's on whole milk if that's any consolation.
Good luck. Your baby will be fine! Remember that it's all about balance, and if nursing is this difficult, then perhaps you need to examine other options.