Talk to Gynecologist on Vaginal Pain During Pregnancy

It is the beginning of my third trimester and sometimes especially at night when i turn i feel crack in my vaginal bone and it makes really difficult for me to sleep and also from the first trimester i got an ache in the left side of pelvic bone and it continues until i take a bed rest... i have a breech baby... does it happen because of the position of a baby? or could it be a sign of preterm labour??