The abdominal cramps is possibly a result of your intestines twisting due to the restricted food intake. I know, because I used to "diet" (starve myself) that way when I was in my early 20s. That daily 500 calorie approach is a brutal way to lose weight... and, from personal experience, I don't recommend it.
By the way, you'll probably notice that by eating, that cramping goes away.
We don't use that type of weight loss method here, since we prefer to use a combination of sensible eating and moderate exercise to lose weight as it's much healthier than trying the "quick fix" methods.
Your husband is more than likely right about damaging your health. 500 calories/day is basically a starvation diet.......
You might try asking your question in the Alternative Weight Loss Forum - I know there are some in that forum who have tried it.
Good luck and feel free to come back and see us any time. We have some great people in this forum who all have wonderful ideas for a "common sense" approach to weight loss. We can also help you with motivation and tons of support......