Shortening of cervix length

I went to visit doc today (am at week 28d5) and doc checked my cervical length and it is currently at 24mm with funneling seen. The last check up 3 wks ago was still at 40mm. Was wondering if anyone experiencing same issue previously and any advice or solution? I also seem to have frequent stomach tightening, and pain at groin area. (baby head has turn downwards) Any sharing or help will be appreciated.