First, I suggest you check out the following blog that includes answers to questions I receive -- http://archcareers.blogspot.
With your degree, you can easily apply to any number of Master of Architecture (3-4 years) for individuals like you that have an undergraduate degree in another discipline. There is no need to get another undergraduate degree. The true challenge is researching programs and developing your portfolios.
To research programs, visit the following:
Also, visit www.portfoliodesign.com for ideas on how to develop your portfolio.