Sakit around pusar during pregnancy tu quite normal, especially bila uterus tengah expand, a few of my mum friends experienced the same around second trimester, tapi memang kena monitor la. Kalau sakit tu sharp, consistent, or ada bleeding/discharge, better check with your doctor cepat-cepat sebab at 16 weeks ada banyak things happening in there. Meanwhile, rest more, avoid heavy lifting, and try warm compress kalau sakit, tapi jangan tahan-tahan, okay, get it checked out to be safe!