Must I repeat the expiation along with the obsessive doubt of frequent oaths after having atoned for them?

What we advise you to do is to turn away from intrusive thoughts (waswasa) and not pay attention to them, and to strive against your soul to abandon them. A vow (nadhr) is not binding except with certainty and is not established except through verbal pronouncement. It is not binding by intention, doubt, or imagination. Similarly, expiation (kaffarah) is not binding through doubt, because the default is the absolution of one's responsibility, and what you imagine holds no weight.