31 weeks and kinda freaking out

Ca

So I'm 31 weeks, measuring 2 weeks ahead by my last ultrasound (3 weeks ago) but now measuring 3 weeks behind by my uterus size. I'm having random contractions (not Braxton hicks doctor said), baby is head down but im not dilated (doctor could feel his head when he checked my cervix), hes still kicking into my ribs like it's his job, and I'm nauseas/dizzy, and in so much pain. Doctor put me on modified bed rest, but im so worried baby is going to come early, or I'm going to be in excruciating pain for the next 2 months. Any advice or just nice words appreciated ❤