Idk what this is!!

I’ve been having Braxton Hicks and everytime I get one it’s like pressure in my back then it goes away when it’s released. I’ve also been feeling this same thing when baby moves. Idk if she’s just laying on a nerve or something but it’s quite uncomfortable. I have to sit a certain way for it to not feel so bad. It’s not pain like cramping so I don’t think it’s contractions it’s just more so in my back and when baby moves I’m 31 weeks. I know I’ve been dehydrated I’m currently on my 5th bottle of water I’m working on that