Stuck at 299

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Well i am new to fitness pal but have been really dieting and exercising:grumble: :grumble: since March 4 2014 and have lost 37 lbs.
I am now having a problem as my weight goes from 299 to 309 for the last three weeks this week i have dropped to a 1800 calorie diet. I work as a forest firefighter so i am very active walking about 3 to miles a day in the fire zone. Any Ideas to help