Mo/di weight at 22 weeks

My twins are measuring in the 23% and 33% percentile. I’m 22 weeks. Is that pretty normal for them to be on the smaller side. My doctor doesn’t seem concerned but going to ultrasounds every two weeks and watching them go down in percentile freaks me out. My MFM also said that he sees my water pushing down on my cervix slightly and has me coming in every week now. My cervix is still long 4.10. But he said he saw the water pushing down on my cervix and prescribed pelvic rest and more rest in general anyone have any experience with this?