It's odd that your kids feel that way too. My son and I just went through something similar 3 years ago.
We had a parasite. It took a double antibiotic to get rid of it.

And years ago I got sick after eating fresh shrimp and I became horribly sick from that too. Nobody could figure out what was wrong. I was finally told I was anorexic. I was so mad. 10 years later I found the parasite myself. (no details, it's gross).

Both times I had to suggest this to the doctor. And the second time I insisted that he take stool samples. I was not going to suffer for 10 years again.
This will make you feel like you do.