If your sure you didn't change anything, your close enough to your wireless access point, and your router is working properly its likely EMI. Do you live close to others? Im thinking one of your neighbors installed a wireless access point and now your signal is interfering with their's. You can verify this with a phone app like wifi analyzer, if your on the same channel as others there could be some interference going on. To fix this just log into your router and change the channel your on.