You probably need a crash-course in the interior design business from the US perspective, and the best place to get that experience is probably in the design department of a Furniture Dealership or Retailer (either commercial or 'home' furnishings, depending on your experience and desires). If income is not your most pressing need, I would start "humbly" and offer to do intern type filing, organizing of interiors sample room, or sales assistance. You will learn so much in 6 months by just listening and paying attention. If you do well, you'll move up quickly...and you will make valuable contacts (who may lead to a job).
It varies by state, but this is what Colorado's rules are:
"The Colorado Architects' Practice Act recognizes Interior Design as a distinct profession and sets out the requirements necessary to call oneself an Interior Designer. Interior Designers are not licensed but are subject to education and experience requirements under the State Board of Examiners of Architects. (12-4-112(6), C.R.S.)" for more information, go to: www.colorado.gov/oed/industry-license/276IndDetail.html
Basically, many states have certain criteria in order for a person call themselves and "Interior Designer"...so be careful there. There is typically NO restriction, though, to call oneself an 'interior decorator'. You do not need a degree or license to work for a designer or under an architect, just don't call yourself a designer. After a few months working in the field in sort of an "intern" type position, you'll have a better idea of how to proceed.
Hope that's not too confusing, and good luck!