The only thing that Alli does it to block about 25% of the fat in themeal at which it's taken. It does not enter the bloodstream and only works in the small intestine.
I can only assume that you are not eating an adequate amount of calories (possibly fat), and not drinking enough water (8 to 10 glasses per day).
It's important that you also follow the pattern of the Sample Menus. They are designed to include adequate amounts of protein, carbohydrate, fat -- as well as a variety of foods - for good nutrition.
Take a look at your Nutrition Log and see if you are under the recommended amounts.
What is the distance of your upcoming races?
I hope this helps.
Pat Baird, MA, RD, registered dietitian