Similar things happened to me after turning 30. I never had oily skin or suffered from acne. I've dealt with dry skin most of my life so having oily skin on my face was totally foreign to me. I started breaking out a lot and most were deep pimples that lasted forever. I tried a good many oily skin/acne treatments and none helped. I stumbled on the Oil of Olay Definity Line and it did wonders for my skin. Wonders. I use the Olay Definity Illuminating Cream Cleanser, Olay Definity Deep Penetrating Foaming UV Moisturizer - Fragrance Free and Olay Definity Night Restorative Sleep Cream. No more oily skin and the acne flare ups have completely stopped.
Skin definitely changes with age so it could just be time to try new product. Trying to find the right ones is a major pain in the ass though.