Back pain- opinions/ suggestions please!

I’ve been having back pain for the past three days or so. I notice it begins after sitting for a period of time. It’s always been in the same location- feels like it’s by my right shoulder blade. It’s a sharp, pinching feeling. Once it starts hurting, I can’t seem to find any comfortable sitting position. A heating pad on warm does not seem to help rid the pain. Any ideas or suggestions? I’m not sure what this may be caused by or how to relieve it. I’ll be calling my midwife tomorrow. 29 weeks today, ftm. I work full time on my feet. Thanks all!