26w4d having dark discharge

Need help. This pregnancy k had on and off brown dark brown discharge. I kind of get scared because I had two pregnancy before and never had this before. Read online it’s caused by sex idk if it’s supposed to be like that since I never had it before on my 2 pregnancies. I have an Obgyn appointment Thursday will have to do the glucose test 😑. Just wondering if this had happen to anyone. I have two girls this one is a baby’s boy very very active. Some lady told me this will be my biggest baby idk how she knows lol but I do feel huge my first daughter was 4.8 second daughter was 6.2 lbs is there a possible way this is happening because this baby is bigger already