Heh
I prescribe a jar of peanut butter twice a day for 2 weeks, then report back with your progress
In all seriousness, you must not be consuming enough calories to cover your TDEE or have an underlying health issue. Might be worth getting the all clear from your GP and if that checks out, maybe consider keeping a record of exactly what you eat and how much physical activity you are doing?
Edit: Sorry, didn't read your post well enough. You're not dropping are you - just maintaining? So you must be consuming bang on your TDEE.