Latisse used for two years - then ceased to work the same and lashes became sparse, brittle, and uneven. Why would this happen?!

My lashes were incredible for two years. Long, thick, dark, full, shiny! These lashes were so gorgeous I never needed mascara and strangers would stop me to comment! Then my lashes stopped growing the same- out of nowhere! They became sparse, brittle, light brown, and very uneven. When a couple lashes fell out there would be a gaping bald spot for weeks. I stopped and waited a year to try again. Latisse didn't come close to working the same as it did the first time. Why is this and what else can I use?