Braxton Hicks or baby moving?

Iris • 🇬🇧 Baby Girl born 16 Jan 2020 💗👶🏻 Baby Girl #2 born 1 April 2021 💗 Baby #3 due September 2023 💙💗

Can some clarify the difference between Braxton hicks and baby moving?

The last few days my lower belly has been getting super tight, not painful just uncomfortable and then I get this bulge on one side of my belly. I thought this might of been baby pushing its head or bum out but now I’m questioning it.... it only last around 30 seconds each time.

Im only 21 weeks pregnant, is Braxton hicks even possible this early on??