Is one expiation required, or is an expiation required every two months for someone who vowed to perform Umrah every two months and then found it difficult to do so?

Scholars disliked conditional vows (al-nadhr (definition) al-mu'allaq) and repetitive vows (al-nadhr al-mukarrar). Nevertheless, one must fulfill them if the condition upon which they were made is met, unless the person is permanently unable to fulfill it. In that case, an expiation for breaking an oath (kaffarat yamin (definition)) is required, based on the Prophet's (peace be upon him) saying: "The expiation for a vow is the expiation for an oath." So, if the inability to fulfill it is permanent, then one expiation for an oath is due if the vow was a single one. Slight or ordinary hardship is not considered an inability and does not permit replacing the vow with expiation.