Help!! Much need advice!!

Jolanda • Sidney Henry IV 💙 10/10/10 Quentin Amaru Henry 💙11/23/11 Kobe Navorro Henry💙 4/26/16 Baby #4 due 9/3/18

So I’ve been having back pains and my discharge has changed from just being milky and thick to watery and milky. This is my fourth pregnancy but I’ve never experienced this before. Am I losing fluid? Am I starting to lose my mucus plug or is this normal for 35/5?