Henry is 9 months old. Some days he is exactly as you describe. Some days he is chilled and relaxed. This unpredictability only started in the last few weeks, so I'm assuming it's adolescence. With the bad days, you've just got to get through to bedtime! I agree with everything daw said. Although I find it difficult sometimes, I ignore the bad behaviour. Rather than giving a time out to the dog, I walk away. I'll make sure he's somewhere safe then remove myself for five minutes. That way we both calm down!
If he's chewing something he shouldn't (which he is suddenly doing a lot of again) I distract, give him something else to chew, instigate a five minute training session or a game. I do say no, and ah-ah, which he knows means stop. As soon as he stops chewing and looks at me (even with his mouth still around whatever he's got!) I offer him an alternative behaviour.
He still play bites in certain circumstances. Belly rubs are impossible, as is sitting on the sofa for some reason.
Don't get me wrong, it's EXHAUSTING, and there are days when I'm just watching the clock until he goes to bed (luckily for me he goes at 8:30 so I have my evening in peace). But other people here assure me it will all be worth it. Eventually.