I am starting to get worried...
 

A little over a year and half ago, I weighed 220 pounds (I am 5'7"). I
quite smoking, stopped eating fried foods, candy, and anything really
bad (started at about 1000 - 1500 cals a day); I started losing
weight and once I hit 190, I started swimming 2.5 KM three days a
week and cycling 20 Miles a day four days a week. I now weigh in at
under 140 and have a good amount of muscle. I also now swim and cycle
competitively. I am now very athletic, but I cannot seem to eat
enough to keep weight on...

This fall I am beginning training for a triathalon event next summer
and so I do not want to give up the exercise for fear of "losing
momentum". At the same time, I am afraid of losing too much weight.

What should I do?