I'm 15 weeks pregnant. I was coughing hard earlier and now I have llq pain when I move or tighten my abdomen. What could this be? Any danger to baby?

Strained muscle/lig. You likely strained some tendons/muscles and/or ligaments in the area causing some pain. If laying still does not cause pain, then it is likely so. If it is hurting constantly, you should have it checked out...