Why can't I take Oxygen Elements Plus?

I think it's also called hydroxygen. I took one drop in a glass of water, even though the bottle says 7. I got the worst stomach ache and bloating. I tried it again the next day and the same thing happened. The stomach pain lasted for several days.

The only thing I can think of is it contains digestive enzymes and the same thing happened. I've tried 3 different brands. Does this mean my body makes enough enzymes?

Thanks,
MG