First what kind of plateau are refering too, strength or size?
Because you dont have to get sore to grow muscle, or gain strength. It's a good sign, and it helps mentally, but its not the final word.
You could do one of two things, either switch up your routine, or take some time off from the gym. A week or two, and just relax, that helps me heal my body sometimes, and get ready for another couple months of working out.