troubleshooting com's transmission

On my first cross-country solo, I observed everybody was clearly
readable by everybody - except nobody could understand ME clearly.
The radio on the club plane is an Icom A200, quite common I believe and
not too bad quality though it is on the cheap side. But I can't imagine
my poor transmission was due to the radio so next suspect is the
antenna, in comes the buzzword "SWR" . Is there a published procedure
for checking SWR on an existing installation?
Any other possible causes? Antenna location perhaps, or lack of ground
plane? But that should show on SWR-verification too, shouldn't it?
TIA,
KA