It must be another one of Murphy's Laws, as soon as we say everything is going great, here comes a problem, right? Thank goodness, this one is fixable!
My recommendation is to try an Eakin Seal under your wafer (if you're currently using Stomahesive paste) and put the wafer onto dry skin (ie - no Skin Prep, etc.)
If you're still having leaks, consider trying a different wafer. There are so many to choose from, and the manufacturers will mail you free samples.
I've been using the Coloplast Assura Extended Wear wafer (item #2833 with matching pouch #13986) for over 5 years and have only had one leak, which was my fault, because I tried to push it past 7 days. They stay on really well and are waterproof and sweatproof. I know... I live in Florida.
Hope all goes well with your visit with the ostomy nurse, and let us know what she recommends.
Dx'd Crohn's in '99 at age 28. Proctocolectomy and permanent ileostomy in '06.
Disease-free and medicine-free since surgery and very thankful to be healthy again.