Belly Button Hasn't Popped!!! Anyone else?

Today I am 31 weeks far along in my pregnancy. I've gained a lot of weight my entire pregnancy so far. I haven't met anyone that has the same inner belly buttons as me. My close friend thats pregnant with me have Her belly button popped out early during her pregnancy! It shows through her shirts and everything . Mine is still really deep. I started showing early between 4 weeks. At 6weeks later I literally woke up one day and had a big belly. Now it's hard as a rock and getting pretty big lol but still no belly button. Anyone else? I'll be 8 months next month with baby #3.... anyone who has experienced this with a previous pregnancy or going through it now? I would really appreciate just hearing your story as I said it's my third pregnancy. I had the same problem with my second baby but with my first baby I don't remember because it's been 16 years and everything has me a worried lunatic lol! Thanks ladies