You need to up your calories. Seriously. Check your Basal Metabolic Rate (http://www.bmi-calculator.net/bmr-calculator/
) and you may find that you're not eating enough. They're usually pretty accurate within about 100 calories.
You can go to 1000 calories a day for no more than 3 days just to kick start yourself again. But honestly, you're doing a lot of exercise; a run, a bike ride, weights and crunches and 1000 calories a day may make you gain or maintain. I went to 1200 a day and did the same thing; stalled for 2 weeks. Went up to 1600, came off. I worked out that for every hour of exercise I did, I needed to up my calories by 100-150. Your mileage may vary; you may need 200 per hour since your body is becoming more efficient at burning them off.
If you don't want to up your calories, look at two thing:
1- what you're eating. Depending on what your diet is based on, you could be eating too much of one thing and sacrificing another. No/low carb diets sacrifice body fuel (carbs) at the expense of eating more protein, which doesn't have enough "oomph" as carbs does. Smart-carb/low GI diets are ideal because they use "smart carbs"- wholegrains, lentils- to help fill you up.
2- how many times a day you're eating: eat 5-6 small meals a day (I'm talking snack-sized meals) instead of 3 big ones. For whatever reason, your body is holding on to the calories because it thinks that it's in famine mode.
Hope this helps.