Shooting pains?

Sunday evening I had slight twinges & mild backache, yesterday I had shooting pains/cramps (almost like gas pains) right in the centre of my abdomen quite low down where I would imagine the uterus to be? I just presumed AF is on her way as I'm due today, but she still hasn't showed & I'm not really getting any aches/pains like I normally would? My nipples have felt more sensitive since last night though? I took my last HPT yesterday morning which was BFN. Has anyone else had these symptoms  & gone on to get a BFP? Could I have implanted late? I think I'm just wishful usual! Lol!