weird discharge after wearing a thong??

I wore a thing yesterday and the day before (don't worry I changed them). I noticed that after a few hours of wearing them, I started to have milky, creamy (but not too creamy), and wet (but not too wet) discharge. Also, it seemed like my cervix moved all the way back, got hard and closed, and my vagina felt really open. I wasn't aroused, but I am on Nexplanon and have been taking some painkillers for surgery I had a couple days ago. Idk if that has anything to do with it. Has anything like this ever happened to you?