Fingernail Issues

Ok, lately my fingernails have been giving me hell.  I usually only have a couple of problem nails, but now all of them are breaking and splitting.  I moisturize them everyday, but that isn't helping.  I have them painted with a clear 'strengthening' polish, but that hasn't done much for me either.

Does this happen to anyone else?  Any ideas for making my nails stronger? 

--Phae