Losing a few extra kilos

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Hi guys, just wondering if anyone has found a solution to what I am experiencing. Last year I lost 14kgs following a strict 1200 calorie plan. Throughout this year I have gained 3kgs back which isn't too bad but 4 weeks ago I decided to try and drop 2kg of that by following the 1200 calories again. This time I have actually gained 1kg!!!! Any ideas for me please. I am assuming it is something to do with a slow metabolism. I run for 20-25mins 3 times a week also.