I've tried hitting him or pinching him back, with less stregth of course, just to get the point across that it hurts
At 19 months a kid isn't near the developmental stage where he can put himself in someone else's shoes. So he can't go from "it hurts when mom bites me" to "it must hurt when I bite other people!". He's just not going to get the point.
But if you bite or hit at all, that just makes it harder to communicate to him that biting/hitting is not okay. He may just think "Mom bites, why can't I bite?"
Okay, some ideas (I'm not a mom, so take this with a pinch of salt, but I work with some kids with "challenging behaviour"). These may or may not fit Mikayle, but see what you think:
Toddlers often hit because they don't have the words to express their emotions, or even to understand the emotions they're feeling. So it can be helpful to acknowledge your kid's emotions and help him put very simple words to them, like "I know you're mad."
And hitting is also a great way of getting a big rise out of adults. Sometimes it doesn't matter whether it's positive or negative, just as long as it's a reaction and it gets him attention. Having a big talk with him about how hitting hurts is a reaction, and so is yelling.
So it's really important to avoid feeding that (and I know that can be really hard when a kid's got his teeth sunk in your arm!). You can be firm, but keep it low-key and really simple: "I know you're mad, but no hitting".
Then try to make sure you're not giving a big reaction. Calmly do whatever needs to be done to stop him from hurting himself or other people - e.g. you could hold his hands firmly to stop him from pinching people, or (where possible) just get out of the way.
If he's really out of control, it can be a good idea to take him somewhere quiet where he can calm down. But that doesn't mean locking him in a room on his own, just taking him somewhere to sit quietly for a while till he can get back in control of himself again (often, all it takes is a few minutes).
This won't work overnight - nothing does. You just have to keep on and on being calm and consistent. If you stick to one plan, then hopefully he starts to get the idea. If you change what you do all the time, it's much harder for him to catch on.
It can also be helpful to "catch him being good". Make sure he gets lots of attention and praise whenever he's not hurting people.
Some links that might be useful: