Braxton hicks?

Ok so I feel like an idiot asking this but this is my third pregnancy and I never noticed Braxton Hicks contractions with my first two, so literally have no idea what they feel like. But lately, when I’m sitting down my belly will get tight and it feel like I’m sucking my belly in but I’m not doing it on purpose, it just happens, and then it releases. But I only experience this when I’m sitting, not when I’m standing or laying down. So I didn’t think this was Braxton Hicks because it’s so positional, but I’m not really sure 🤷🏼‍♀️. Do anyone else’s Braxton Hicks feel like this or happen like this? What does everyone else’s Braxton Hicks feel like?