Nabothian cysts like this are very common and usually harmless. They are small mucus-filled bumps on the cervix that many women have, often picked up incidentally on a scan. Letrozole does not typically cause them, though the vaginal dryness you noticed is a known, reversible effect of how it temporarily lowers estrogen.
Next Steps
The cyst usually needs no treatment on its own and often stays unchanged or shrinks with time. A vaginal moisturiser or lubricant can ease the dryness until your estrogen levels settle after stopping letrozole.
Health Tips
Since two cycles have not led to a pregnancy, please see your gynaecologist about your PCOD and the next fertility steps at your upcoming visit.