My personal experience with lag is due to the overload coming from my ISP and the fact I have serious packet loss. Whenever I play at night on eastern time, it's where the rush hours folks from central/pacific.
But since it's only the last few days, I would check if the modem/cable are at fault. Conisdering the fact that in IT world, network problems usually ends up in the first physical layer.
(/OSI layer reference joke)