Help me lose 15 pounds!!

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Hi! I'm new to using myfitnesspal and so far I like it. In January, I weighed about 125 pounds, but after having mono, developing what my doctor thinks is a hormonal imbalance, and traveling, I'm now up to 137- the heaviest I have ever been. I'm 20 years old and 5'6" and I'm aiming to weigh 122lbs but I'd like to get down to 125 before I go back to college in September. I work out everyday, usually running about 2 miles and walking another 2-5 miles. I also used to lift weights but haven't renewed my gym membership and am thinking about doing insanity. I always thought I was overeating, but now that I've started mfp I see I actually have trouble reaching the 1200 calories after exercising. How important is it for me to reach that everyday? Any suggestions on healthy calories I can eat to reach it?