Caveat: I am premenstrual, so this is bugging me extra hard right now but it's been going on since before my DS turned 11 in the summer.
I get that he's started to develop earlier than I expected (thought I'd be dealing with this around age 12/13 so I was kind of caught on the back foot) and is hormonal, but my 11 year old has been a little git lately. He started wanting privacy about a year and a half ago, which is perfectly fair enough. He's got spots, body changes, his voice is starting to get deeper and the sex ed book I got him prompted him to google porn (aaaaaaaagh) until I realised and had a chat with him. He just wanted to know how sex worked which I get but I am horrified by what he has seen.
But the main ongoing thing is his attitude is horrible a lot of the time. I remember being a bit of a shit to my mum at age 11, but it's so wearing. It's not the content of his words but the attitude and disrespect, it gives me the rage.
He was previously impeccably behaved almost all of the time and was only ever like this when really tired. Now it's constant. I'm a single mum and am so fed up of being talked down to. I'm normally relatively strict and not a lax parent but it's so exhausting always having to be on my guard being he's horrible or rude so much of the time. I've started to feel relieved when he goes to his Dad's (50/50). His Dad supports me if he is rude to me in front of him and he is less like this with his Dad as he wouldn't bloody dare - so I get it all.
When he's not being horrible, he's lovely. He still this smart, funny and kind person underneath that I love so much. But it's like hormones have changed his personality. 
Tell me it's not just my 11 year old...