Alamak, yang tu mmg biasa lah sis! Baby position dia selalu bertukar-tukar lagi especially baru 12 minggu, could be ubah posisi, or placenta position dia yg buat terasa belah lain. A few of my mum friends juga cerita sama, denyut kat satu side, then next week lain pulak, haha! But since you're seeing a change and it's making you wonder, best check with your gynae just to be sure, takde salah kan, diorang boleh tengok terus letak placenta dan baby kat mana, and confirm everything's good. Jangan stress lah, usually perfectly normal je.