I think that everything you have said sounds entirely normal and nothing to worry about VANESSA.
I've got two busy, sociable daughters so no personal experience to add but thought I would tell you about my friend's son who never ever had anything on and would never ever pick up the phone and organise anything, ever. My friend worried and worried about him.
Even when he was eighteen and in the Upper Sixth, my friend was tearing her hear out because he genuinely had nothing at all to do unless she organised it for him.
She occasionally organised for him to get together with another boy (of the same ilk!) via his Mum (also tearing her hair out). She pushed him to do Scouts and DofE to keep him busy and push him in with other people. She also organised for him to volunteer at our local wind-surfing club all summer one year as a helper with the little ones. But, otherwise, he was sat at home on his Playstation on his own.
Two and a half years ago, he went off to university and she worried herself sick that he would sit in his room on his own, make no friends and that at the end of the three years no-one would have even heard of him.
I'm happy to tell you that he joined a few societies in week one at university and that his life took off.
Now, when he comes home from uni he almost always brings a friend or two with him or has friends arriving to come and stay after a few days. Or he can't come home because he's off to some party or birthday bash or trip or whatever.
It's a huge, happy relief to my friend. Maybe he just needed a fresh start but I think people just mature and develop in different ways at different times.
To be fair though, I also think it's difficult at school because there are only so many people in your year to choose from - this is why outside and extra-curricular stuff can be so important, in my opinion
Hope this helps 