Extreme back pain 38 weeks

I was fine over the weekend, then monday night I walked to my friends house and then back, I was probably only walking about 20 mins total, so not much. By the time I got back home my back was starting to ache, I had dinner then went to bed. When i woke up yesterday i could barely move my back was just so tensed up, so i ran a bath and tried to relax but it was so painful. Its now wednesday night and its just worse, my boyfriend has to pick me up to help me get off the bed, i have to grab the walls to help me stand from the toilet and stairs are not even an option, I havent been able to get downstairs all day without being held by someone. I cant even lay down without nearly crying. I had a midwife appointment yesterday and she said its just where im bigger out the front its straining my back, but why so suddenly 😩 I have such a small bump aswell I cant see why it would be straining me. im 38+4 weeks.. anyone have any ideas on how I can make this ache go away a little?