Hello! I work in the fashion industry, and have friends in the architecture/interior design industry. So, for a little outside perspective, I would recommend first figuring out which aspects of building and fashion design you are most attracted to. Is it the aesthetics? Is it working with people? Knowing the upcoming trends? I would look into getting a part-time job as a retail sales associate in a store you could see yourself working in, either fashion or home goods. See if you like it, and maybe it will help you figure out which direction to go in. As far as going into a field as specific as Interior Design or Fashion Design, I would definitely do research on actual job outlooks. Both of those are very specific and very limited, especially in a down-turn economy. That being said, you may also want to look into jobs within those industry's that are always in demand. Wholesale for fashion is always looking for new comers, working in showrooms, doing product development, or visual merchandising... All of these are great, fun careers you can pursue in either fashion or interior design fields. I went to FIDM, and I currently work there. I would definitely suggest taking a look at their majors. The Fashion Institute of Design & Merchandising is an amazing school for anyone interested in both those fields. So is the Fashion Institute of Technology in New York, or Harrington School of Design in Chicago. Just explore your options, and dig a bit deeper. There are way more avenues to go down if you want to be involved in fashion or interior design than just the obvious.
Hope that helps! :-)