I have some chickens and I can't figure out why they aren't laying like they should.?

I have a flock of 40 Rhode Island Red hens. I got them this past spring and I don't know why they aren't laying eggs. I am only getting about 7 eggs a day. They are in a pole shed where they do get some sun exposure. I am feeding them the same fed that I fed chickens from past years. The diet consists of 5 scoops cracked corn, 1 scoop 16% poultry layer, one tin can of oyster shells per 5 gal. bucket. I feed around half a 5 gal. pail per day. I do chores about 3:00 in the afternoon. I have been raising chickens for years so I don't know what is happening. Any insight from people with experience would be appreciated. Thank you