A couple of thoughts about this:
(1) To determine if the problem is subject movement or lens diffraction, zoom in on a flower stem or a petal edge; 200% or more. You should be able to see if the blur is side to side or a halo look. Side to side is movement while the halo look is a lens issue. I'm not familiar with your lens, but with my Nikon 60mm macro, I use a lens hood even though the front element is recessed. Stray light will reduce contrast and could make an image look more unsharp.
(2) Diffraction at f22 will be a problem regardless of the lens. Although with a true macro lens it will less that with a "normal" lens with a macro feature. Find the "sweet spot" aperture for your lens. There are lots of web pages on how to do this, but the general rule is that the 2 mid range fstops are the sharpest. If you stopped down to utilize a slower shutter speed, you can either use a lower ISO setting or use Neutral Density filters. Get the best ND filter that you can afford. You may also want to get several different density factors. 1stop, 2stop, 3stop. To minimize the wallet shock, you can get the biggest filter needed to cover all your lenses and use step down adapters.
I assume that your looking at your images after processing and have sharpened them.