I’m going to go out on a limb (not really) and bet that your list of supplements doesn’t include magnesium. But it really should. It’s essential for good sleep and heart, muscle, and brain function—all of which impact your abs— and yet research shows most of us aren’t getting enough of it.
An analysis in the Journal of Nutrition Reviews revealed that 48–60% of Americans don’t meet the recommended daily value for magnesium, which even then is only considered the absolute minimum (a great physique likely requires more). Add a magnesium supplement or a multivitamin to your diet and see how your results improve.