A plateau is totally normal - your body adapts to the stress. If nothing's moving for two months, it's time to change something in your program. The key thing is, it's not just protein that matters, but calories overall. Check if you're actually eating enough to build muscle, not just "not losing weight." A lot of people after half a year are already eating less than they need because their body got used to their current diet.
As for the training itself, two months on the same weight means you need to vary your exercises. You don't have to drop what's working completely, but add different angles and grips. For example, if you're doing barbell bench press, try dumbbells or incline press at the same time. Sometimes it helps to just change the order of exercises in your workout or increase the number of sets instead of the weight - volume sometimes breaks through a plateau more effectively than chasing heavier weights.
Also check your recovery: are you sleeping properly (at least 7-8 hours), how's stress? After half a year people usually get mentally worn out, workouts turn into phoning it in. If you're just spinning on the same weight, your body has no reason to grow. Try dropping the weight by 10-15% for two or three weeks but doing the exercises with higher volume (more reps or sets), then go back to your working weights with renewed strength. It often works.