Just curious and definitely not trying to be rude, but you said you stuck with the plan, yet you say "Too much exercise and not enough food" which is probably why you're getting headaches and dizziness.
Even though I'm on the 6 Week Body Makeover plan, I eat all day every 2-2 1/2 hours and drink 100 oz. of water and am NEVER hungry, Alli's food plan is a lot of food to eat also and good food at that. You've gotta protect your body.
As for the Vitamin D deficiency and sometimes Calcium, my doctor told me mine was low, too, but she's told me that forever and I'm listening this time and adding it with my nightly vitamin regimen. I hope you don't quit taking Alli. I really think you need MORE FOOD (small shrimp w/greens and a little dressing for a snack) (which is always good.)
Take care.
Starting Weight Before Alli: 175 lbs.
Current Weight: 164
Goal Weight: 136
When in doubt, dial 911!