Sakit perut macam tu memang boleh jadi normal dalam pregnancy, tapi sebab location dia berubah-ubah dan tiada quickening lagi at 16 weeks, mesti check with your doctor to be safe, better to get reassured daripada worry, kan? A few of my mum friends had similar aches during second trimester, tapi ada jugak yang turned out kena constipation je (very common in pregnancy!), so it really depends. The pain shifting between pusat and muka sisi tu, plus the heaviness feeling, boleh jadi ligament stretching as baby grows, but since you're also worried about no movements yet, doctor kena check proper. Don't stress yourself, at 16 weeks quickening can be subtle especially if first time, but get a check-up to put your mind at ease, okay?