Generally, your body will adapt if you use the same program without changing any of the variable such as intensity, volume, or exercises. How long it takes someone to adapt to a particular program varies from person to person. You could always try adding a few more lifts per body part as you suggested or you could change up the rep ranges you are using. Also, you could try adding in something like drop sets to up the intensity. You could also just reduce your rest periods between sets. There are lots of adjustments that you can make to your current workout to keep your body guessing without creating a whole new routine from scratch.