Eh sayang, kat 16 weeks baby gerak memang baru-baru ja boleh terasa, so yang sakit tu mungkin mixture of baby movement, gas, or just ligaments stretching, first pregnancy memang banyak rasa benda aneh kan! Tapi since you're describing it like gastrik, best to message your doc or midwife just to confirm everything's okay lah, especially kalau sakit tu naik turun. A few of us pregnant mums had similar feelings and turned out fine, tapi better safe than sorry, particularly if it's accompanied by other symptoms. Take care of yourself, mummy!