I am pretty new to minecraft, I started playing about 2 weeks before 1.8 was released. I am having a problem now where monsters spawn in my house when I am awake and working on other parts of my house. I have no problem sleeping, I don't get monsters then. I might be down a level working on a basement and then come up the stairs to find a two creepers on the way down to say hello. The last time it happened, they spawn on the top level of my house (which was 3 levels) I went through and made sure all the walls were 2x thick and had plenty of lighting. I am not sure if this was a bug but it started happening after the 1.8 updates.
You need to light it up more. Set the light setting to moody to see where more light is required or DL the mod that adds a light counter in the top left corner. Or just turn of mobs.
My computer specs:
Intel Core i5-4690K, Asrock Z97X Killer ATX Mobo, Corsair Vengeance 16GB, Hyper 212 Evo, GTX 1060, EVGA 750Watt PSU, 840 Evo 120GB SSD, 1TB WD Blue, NZXT H440 (black/red).