Preterm labor?

How did some of you moms know that you were in or going into preterm labor? Were you scared that you maybe you were overthinking if it wasn't too obvious (like water breaking). Please tell your stories. I'm having lower back pains and every so often I get cramps like I'm going to have diarrhea. Please help 😰

Edit: this morning I also had a lot of pressure in my pelvic region and it felt like my baby was going to fall out. My pains are constant