Very light brown discharge @ 22 weeks

Light bleeding or spotting (which can be brown, pink, or red) during the second and third trimester isn't usually cause for concern. It typically occurs as a result of interference with the cervix during sex or a vaginal exam. Pink mucus or brownish discharge may both occur during the second trimester.

Consult with your OB at once. I experienced the same. It started with light brown discharge then eventually became darker. My OB said it was because my cervix is open. She advised bed rest and gave me medications to prevent miscarriage