lost 9lb in 4 weeks worried about hitting plateau

itsskyhigh

I've been on a doctor recommended and monitored 1200 calorie diet. I dont really have a diet plan. Other than eat as much protein and fiber as possible within the 1200 calorie range. I eat different things everyday. But I use almond milk instead of whole. I eat fat free yogurt when I want something sweet. I avoid ramen noodles and mac and cheese and those sorts of things.

I lose 2-3lb a week I was 167lbs now im 158lbs im 5'3 btw really happy with te results but im terrified of hitting a plateau. My goal weight is 120lbs my doctor said once I get to 130lb-140lb range to start doing toning exercises and increase my intake.
What can I do to avoid plateau?