Baking soda can lose it's fzzz. Baking powder can lose it's leavening ability as well. The oven thermometer is also a good suggestion. And did you by chance change old measuring equipment for new?
I had set aside an old set of measuring spoons and cups. Purchased new. Nothing would come out right and I also lost lots of dishes, they tasted horrible and were extremely salty. Checked the new measures to the old and found out the new were not accurate! Had to throw them away. Now when I purchase new measure equipment, I always check for accuracy against my old old old set.