Training & Nutrition - How to tell if I'm eating too little?

Just making sure that I'm clear, I'm not anorexic at all but I have lost about 20 pounds (mostly from cycling, 210-190lbs). Now, I'm feeling pretty good and healthy but once I've gotten to 190 and plateaued out, I've been eating very little lately (it have coincided with my running out of money so I had to eat less anyway). Eating less is usually no problem for me since I've always ate too much at most meals in the first place but in the last week, I've only had 1 meal a day (2 meal a day yesterday and today so far). I do drinks a whole lot of water but I still worries that I'm getting too close to eating too little.

So here is my question, How can I spot any under eating issue? are there some kind of usual symptoms that I can check for in the future?

Loss of weight, muscle mass (coincides with loss of weight), feeling tired.

Assuming you're still losing weight, make sure the weight loss isn't too rapid. You shouldn't be losing more than a pound or pound and a half per week. If you're dropping weight faster than that, adjust your diet accordingly.

try eating at any fast food restaurant and you wont have to worry about it

How do you know you are under eating--I had this problem when I started cycling. I had just lost 30 lbs and was plateauing. I kept my food intake the same. At the end of my Thursday group rides I found I could barely make it up the last hill. The next Thursday I had a lunch significantly larger than normal. That same ride the next week I had plenty of energy to finish the ride. Basically if you are too tired at the ends of your rides, try eating a little more next time.