Ahhh don't worry lah, baby kat dalam air/amniotic fluid so cushioned sikit, tidur atas perut atau tertindih sekali dua tak akan bahaya sangat, tapi memang lebih safe kalau tidur sebelah je lepas 4-5 bulan, badan baby dah besar sikit. A few of my mum friends had the same worry and their doctors said it's fine especially early pregnancy, tapi kalau sakit perut terus pastu ada cramping yang tidak normal, better check with your OB just to be safe