My advice would be to take a full spectrum digestive enzyme supplement with your meals - especially protease, but also lipase and amylase. You may not be digesting your nutrients well, including all those supplements you are taking, and particularly protein.
I know "take another supplement" isn't necessarily what you want to hear, but I say it because I used to have soft, weak nails that would break off, and my aunt (who is into nutrition) recommended digestive enzymes. And what do you know? My nails fairly quickly became really strong.