Son is struggling badly with loss?

Earlier in the year, we lost our 3 year old son to cancer. It hit us all hard as a family. I was pregnant when Callum died and have since had the baby, we are all trying to get on with our lives. I am most worried about my oldest son, he's 11 and just started secondary school, he's always been quite a bright boy, but he just doesn't seem to care anymore, it takes persuasion for him to do his homework and even at that he just scribbles down answers quickly, he doesn't try. He's seeing a councillor and she tells us the only time he's truely happy is when he's playing football, this worries me because of course as parents we all want our kids to do well. I am at a loss of what to do, the school are aware of our situation and are giving him all the extra support they can, but he just doesn't seem to be getting any happier. I would greatly appreciate opinions from youths who may have experienced similar situations, or just have any ideas, thanks so much