Are there specific supplications or remembrances (dhikr) for conceiving, and is having intercourse two or three times a month considered unlawful, especially since I strongly desire to conceive?

Sexual intercourse has no specific times, and the matter depends on the husband's activity and the wife's desire. The spouses should strive to make each other happy. The husband does not sin if he leaves off intercourse for days or weeks, but he may fall into difficulty if the period exceeds four months. This is a right of the wife, derived from the story of Umar ibn al-Khattab with the woman who complained about her husband's absence. Imam Ahmad specified this period as four months, based on the duration of al-ila' (a vow of abstinence).