My DS nearly 12 has lost interest in sport apart from once a week footy with his mates, and is always tired. He prefers to do things sitting down like using his tablet (of course) reading, drawing crafts. We have offered him the choice of trying other sports or clubs but he doesn't want to. He has lots of friends and is doing well at school. He has just started puberty but only just. Is this hormones or something else?
Make sure he has some red meat in his diet. I had long spells of tiredness at that age due to iron deficiency. Then again I'm a large lass and had my period already, but I suspect it had a lot to do with growth as well.
This sounds like my DS a bit, he's 13 and he just sits around all day, he gets tired from just walking very short distances and he too is constantly gaining weight, no puberty yet though. Maybe it's just a lack of interest in activity rather than energy ?