During the third trimester of pregnancy, it is common to experience stomach tightening or Braxton Hicks contractions. These contractions are usually irregular and painless, preparing your body for labor. However, if you notice frequent or intense tightening accompanied by other symptoms like vaginal bleeding or severe abdominal pain, it is important to contact your healthcare provider as it may indicate preterm labor. Stay hydrated, practice relaxation techniques, and change positions to ease discomfort caused by these contractions.