Pre term labor or BH?

I am 17 weeks 5 days today. I felt my babies first kicks at 16 weeks 3 days. I got to SEE the movements at 17 weeks 4 days. I am a first time mom so it's all new to me.... since the day I was first able to feel the kicks, I've also noticed a change in my lower abdomen. Very very low I get these solid rock hard moments. It's like my pelvis region becomes a brick. I can not only see it, but for sure feel it. However, there is zero pain. There's isn't much "discomfort" either, it's just very strong and noticeable how tight and hard it gets. A best way I can explain it is it looks/feels like a speed bump (lol) orrrr like a ocean wave tide beginning in my "area" then rushing up to my belly button, then it perteudes out and becomes hard. They last about 30 seconds- 1 minute probably, and it's throughout the whole day So this has been happening for about a week and a half now. Also, I still can few my baby moving and kicking after it softens back up and sometimes she will move fully on one side and I can see that she's balled up on my left because my belly becomes lopsided. Also I have EXTREME BACK PAIN

What is this? Normal? Should I be worried?