Pressure/pulling in uterus

I’ve been feeling a pulling/pressure feeling on what I believe would be my left ovary since last night 12 dpo. It’s on and off. I also had a horrible headache yesterday that came on randomly. Might this be a sign of implantation? My period is due today or tomorrow. No sign of her yet. Hoping this is a good sign, although I tested this morning and it was negative. 😢

Hoping to hear your stories? If anyone had anything similar to this?