Hullo Periwinkle
Sounds like you're both having a tough time, my heart goes out to you! One thing knowing it's a normal phase and emotion, but it does feel hard when it's your LO and it's directed at you, and nothing you do seems to help! My DS is newly 4 and we've just been through this very same phase, so I wonder if any of the stuff that helped us may help you too. We have come out the other side intact, and even more closely connected than before, so I hope that gives you a bit of hope.
I had the usual advice about time outs, ignoring, punishment/reward etc. that you seem to have tried. But they seemed to be punishing him in one way or another, just for having feelings which he didn't yet understand and impulses he couldn't yet control, (which we all have and god knows even adults can't control properly). But there were quite a few things on line, that were an alternative to all that, and which were the things which really helped us come through it.
There were some ways of understanding what was going on for him, and tips and techniques, that were particularly helpful, so a few links below are for you to have a read through for you to check them out if you're interested. (If you can stick with some of the Americanisms I did find it worth it - and they explain what I found out far better than I could even attempt to explain in a post!)
www.ahaparenting.com/parenting-tools/positive-discipline/Child-Hits-parent
www.handinhandparenting.org/article/children-hitting-biting-pushing-helping-children-with-aggression-2/
www.janetlansbury.com/2014/07/my-preschooler-is-hitting-me/
www.positiveparentingsolutions.com/time-out/transform-your-time-outs-to-time-ins-guest-post-from-dr-laura-markham
www.ahaparenting.com/parenting-tools/positive-discipline/effective-limits
The other thing that was a complete godsend was the book 'How to Talk So Kids Will Listen and How To Listen So Kids Will Talk', by Adele Faber & Elaine Mazlish. I'm not one for parenting books, experts and 'gurus' at all but, I was at a loss myself otherwise, and gave it a go. It was £6 online and the best £6 I've ever spent. Dead readable, could dip in and out of it, and every bit of it helped,especially the chapter on empathising with your child's negative feelings. That made us turn our first corner from a biting, kicking, slapping, punching, shouting, screaming scratching, defiant little boy, to a scared and angry little boy who turned to his mummy because he knew I'd listen to him and that I'd do my best to understand him, to a happy, confident, cooperative (mostly - he's 4!), empathic, kind and secure little boy. So, not quick fix, but for us, it worked.
So good luck, lovely. Sorry for massive post but I hope perhaps our experience might help you both move on to a much happier (and less defiant and hitty) place xx