I've hit a plateau! Any sugestions?

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Hey! My name is Catherine and I have successfully lost 26lbs (starting weight 14 stone 8 lbs, now 12 stone 10lbs). I've reached a plateau and although I don't think I've changed my diet much and am continuing to work out, I have not lost any further weight.

I've been told to mux up/ intensify my workouts, which I started today but I do not want to cut down on calories as I'm currently eating approx 1200 cals daily so do not want my body to go into starvation mode hence inhibit my weight loss. Any advice? I wana lose at least another 26lbs to have a healthy BMI. Thanks in advance for any help :)