Have an Answer?
I would start by answering "why can't I be a fashion designer?". Is it because you're no longer interested? No opportunities out there? Have you done everything you can to come up with the answer "I can't". If not, then I would advise you give it your all. If then you believe you cannot be a fashion designer, then see what other careers there are out there that can benefit from your skills in design or fashion (perhaps a personal fashion assistant, working for an industrial company as a designer, or even just as an advisor). I challenge you to think outside the box and find something your passionate about, and run with it!