Lower abdominal pain. frequent urination. hurts to pass gas feels like it's being trapped. what could this be?

Many things: Lower abdominal pain in a woman could be from the bowels (e.g. constipation, irritable bowel, diverticulitis), the urinary tract (infection, kidney stones), ovaries (cysts, menstrual pain), uterus (pregnancy-related, menstruation related, endometriosis, sexually transmitted infections). A detailed history + examination + urinary test can help diagnose the majority of these possibilities.