is it right to say "i didn't receive an invite"? or should it be "i didn't receive an invites"
Strictly speaking, yes, but invite is increasingly used as a noun these days.
Invite = verb (invitation=n.)
Students: Are you brave enough to let our tutors analyse your pronunciation?
 nona the brit's reply was promoted to an answer.
invite is an informal way of saying invitation.

is it always with an s or not? singular-invite plural-invites? am i right?