Is 500 mg of caffeine every 4 hours a lot (total 1,500 mg)

In a controlled tablet form?

I just took my first 5 pills (100 mg) each.
http://www.nodoz.com.au/faq.php

I'm trying to keep myself from sleeping during the day, and curb my appetite.

Thank you.

Considering an average cup of coffee has about 100 mg of caffeine, one of your pills is like drinking 5 cups of coffee. You are probably overdosing yourself for appetite suppression. And, by the way, studies have shown that too much caffeine during the day can interfere with your sleep at night, so you'll still be sleepy during the day - and get yourself into a vicious cycle.
Plus caffeine as some ill effects on your blood pressure. Whatever you are trying to do, you won't have long term success with this plan, and possible make matters worse.
Try some chamomile tea at bedtime, sleep better, feel more awake during the day, and try a more sensible diet.