Ay, hindi ako doctor kaya hindi ako makakaassure, but maraming tubig sa tyan during pregnancy can sometimes mean something needs checking, best talaga na i-ask mo agad ang OB mo about it, lalo na kung may sinabi syang concern sa ultrasound! One of my mum friends had similar situation at sinabing just monitoring lang needed niya, but it really depends sa amount at other factors na kailangan tingnan ng doctor mismo. Don't worry too much muna, pero get it clarified na agad para matulog ka ng mahimbing.