Feeding 4 month old

okay let me start with this. i dont care what you have to say about the solids. his pedi recommended it and approved it. moving on... my son is 4 months old, 5 at the end of the month. I've been giving him about an ounce of oatmeal once a day. Up until yesterday he was sleeping fine. Now he fights his sleep for hours. yesterday we was awake from 6am to 5pm. YEA. so I'm wondering if it has to do with the 4 month regression i hear about or the baby cereal