Memang common la rasa sakit memulas macam tu masa pregnant, especially kalau perut kosong atau selepas makan benda tertentu, a few of my mum friends experienced the same around mid-pregnancy. Tapi since baru terasa selepas ambil ubat tambah darah, boleh jadi ubat tu agak strong untuk perut, or your body just adjusting to it lah. Better check with your doctor or midwife quick-quick to make sure everything okay, terutama since it's happening repeatedly, biar dia dapat tengok and advise properly ye!