Oracle Database Express Edition (XE)

i'm trying to insert some values in my table but i'm getting this error:
ORA-00917: missing comma

i'm using php and the query is like this:

$insertar=oci_parse($conexion,'insert into medicos (fecha-presc,ciudad_presc,nombre) Values ("17-04-2010","mexico","Fulanito Mayor")');
oci_execute($insertar);

what coul be wrong??

i created a sequence and a trigger for making the id_medico field auto-increment...


thanks !!