Excruciating pain contractions!!

I just started this new bc depo I haven't been on it in over ten years.... Instantly upon my cycles start date no period. Haven't had one yet and it's been two weeks already made sure I wasn't pregnant but I have some strong uterine pains that come and go in waves like contractions would do u think my body is trying to ovulate but is conflicting with bc or is it my body just reacting to not having a period... Idk anyone else know why my uterus and lower abdomen could be causing so much pain??? Any guesses ???

like when they come I have to put my face in the pillow so I don't scream and wake up my kids it's so painful.