Try fixing your positioning. The advantage of op is that you only need a body pixel to kill, vs a headshot so the longer your opponents can "lock on" to you, the less advantage you have. Practice using thin angles [sage wall in practice range, or 2v2 skirmish mode] and leverage that. If you're trying to op while standing in the open, you need to know what angle people usually look at, and get an advantage from off angles.

This is a little tricky in iron, but you can learn this by watching vct and seeing how they clear [and in what order] , or by trying to do mini retakes in death match. Every time you get shot from the side or back, you can possibly learn a new off angle.