Needed some advice

Hi recently i had brown discharge but just a light one but dr told me that i had short cervix length but after done with ultrasound to confirm, its 3.0 to 3.1cm within the range but dr still gotta monitor. Dr prescribe me with Progesterone tablet and Erythromycon tablet and injection too. Any mummies right here had the same issue w me. Im so scared if i had to go through preterm birth. This is my first pregnancy though 😔