I think maybe it's the cooler weather too
He is maybe trying to dig down into the substrate and make his house cosier. As Pink Neon says, just give him a load more bedding. Torn up strips of plain white toilet paper are best. They pouch it, take it to the nest and make a bigger cosier nest. If his house isn't that big you could maybe add more substrate as well, so it's deeper and he can burrow down a bit. We've started leaving a little oil filled heater on low at night as the nights have been cold recently. As they get older I think they feel the changes in temperature more.