At 17 weeks, some of that could be baby movements na parang mga pinches or flutters, pero yung masakit na feeling combined with the back pain when lying flat is something I'd really suggest you check with your OB about just to be safe. A few of us mums felt similar things at that stage, pero kailangan sure na walang ibang nangyayari, especially if the pain is bothering you, better peace of mind, diba?