Pressure

So ill be 38 wks tomorrow. And all day ive been feeling pressure in my back and it will feel like i have to poop or fart and when i try nothing happens. What could this be? Last time i was checked at 35wks and i was 3cm but ny cervix was thick. This is my second baby but with my first i was induced due to preeclampsia so i never experienced this. Any advice or suggestions will be very appreciated! TIA