I really feel you on this, that tight, heavy feeling can be so unsettling especially when you're not even showing much yet, but from what I've heard from other mums, it's actually very common at 17 weeks! Your uterus is stretching and growing quite a bit around this stage, so that hardness and heaviness is usually just your body adjusting, and most mums find it eases off after a day or two as the muscles get used to the change. My friend went through the exact same thing with her first and mentioned it was partly Braxton Hicks contractions, which can actually start this early and make the bump feel rock hard most of the time, as long as they're not painful, it's generally considered normal. That said, since every pregnancy is different and you're feeling uncomfortable even when lying down, it's really worth bringing this up with your gynae or doctor just to get proper peace of mind, okay?