Exclusive Pumping

I am a little over 6 months into exclusive pumping and its been going really well. Solid supply, fee like i am emptying well, and have never had an issue with clogs or engorment. Ive been on the same pump schedule (4 times a day) for over a month and am very consistant with it and it works well for me. The last few days out of nowhere i am starting to feel engorged before my usual pumping time. To the point where sometimes i need to pump a bit early and it throws off my schedule. I am still emptying during every pump (it feels like at least) so i cant figure out whats causing the pain. Has anyone experiences this or have tips or ideas to help?? Hoping to keep going til my sons is around one so not ready to wean yet