48 does sound way too small UNLESS OP is quoting the ACTUAL seat tube length rather than the nominal size or EFFECTIVE seat tube length. A few bike makers are listing their sized by ACTUAL seat tube which is much shorter on a compact frame then EFFECTIVE seat tube. But fit is all about the individual bike chosen, not some number listed in a table. Try to understand what the size number means. For 5'6" an EFFECTIVE seat tube (going from the bottom bracket center to the top of the imaginary top tube if it were horizontal should be around 50-53.