Gardner, who is out of date and completely unreliable on attributions, has an AE6 ( I'm not sure he's metric, so beware) of 'Vologases II' with a pointed beard and a winged
caduceus in a dotted square on the
reverse. The type's not shown on
Parthia.com as far as I can see at a quick look, but the
attribution may translate as Vologases I. You're coin diesn't look like this one, and I'm not sure it's a
caduceus either. If it is, that would suggest
Roman influence, so possibly
Armenia? I've no idea about their coinage, but they
had Arsacids as kings, and there's lots of
Roman influence there, so it could be.