Hi sunshine,
I can so sympathize. Was a time I went into an uncontrolled weightloss spin (due to intenstinal disorder, in my case). I kept looking for weight-gaining diets, but all the well-publicized ones are about losing more, never about putting some back on. I "bottomed out" at 50kg and I'm 5'9", so you can imagine how little muscle I had on me! I ended up getting help from a nutritionist. Turns out I had lost some key nutrients that had to be gained back -- along with getting the disorder under control, of course -- then the weight came back on. In fact, I overshot the mark but was too nervous about over-losing again to do anything about it until recently. Now I am slooooowly inching my way down where I want to be. Slowly seems to be a key here. So my advice:
1) Don't be too stressed out and impatient about this. Work your way gradually back to where you feel you should be, and listen to your body along the way. You want to put on muscle, not just fat, so you'll need to eat just a tad more than you're burning and keep on working out.
2) Talk to a nutritionist, if you can.
3) Take the time to enjoy your food. Make it look good and taste good. Have nice music on, or a good book handy -- whatever makes it more fun. Eating is not a duty, it's a pleasure. You eat because your body wants to eat, not just because it's the sensible thing to do. So take the time to listen to your body thanking you for the good food.
4) You might want more than 3 meals a day. Multiple smaller meals rather than 3 big ones are less likely to leave you feeling stuffed and uncomfortable.
5) Maybe prepare several meals in advance, so you don't get tempted to skip or postpone meals just because of the time and effort of preparing them.
6) Take along energy snacks when exercizing, and remember to eat them. That's in addition to your regular meals. If you're undernourished, you may be "bonking" regularly and taking that to be a normal state of affairs. That could perhaps explain the tiredness and weepiness. Also a burst of extra energy here and there along the race or ride may give you back some of that speed you're missing.

Good luck to you! Recognizing that you're running out of power and that it may be related to the weight loss, that's a good start. And you're also addressing the problem by eating more. Stick with it and you'll get back in shape, maybe better shape than ever!