Trying for baby number 3

Me and my love been trying for baby number 3 for a year a half i pose to got af on the 13 and nothing i had a couple apps say the same thing as glow and 1 or 2 say the 15 but im pretty sure glow is right but i been cramping real bad like af is coming but these cramps hurt real bad all in my lower back and legs so it has me on a pause to test i was gone wait and see what today does because the cramps im getting are on and off but hurts when it do come like af cramps what has this happen to anyone else or advice thanks