Why Do I Have A Recurrent Bump That Appears On The Left Side Of My Cervical Area?

Hi I have a reoccurring bump that appears on the left side of my cervical area. The bump is visible, soft and tender. It usually Lasts for a day at the same date of each month then disappears. I have asked my obgyn and didn’t get an answer. Could you please tell if this condition has a treatment. I’m worried. Thank you