Pressure to..

So I’m 36.4 weeks pregnant with my first and been having preterm labor! I been having low abdominal pain and pressure like because he is low and back pain which I know can be labor pains but I have been using the bathroom (#2) more frequently but not diaherra but loose to easily go! But since I came home from dinner at seafood restaurant I been having the urge to go #2 but I can’t like I feel like I have too but I can’t !! Why? Have any of you experienced before?? And my pain down there like it hurts to walk or lift my legs .. normal??