What Causes Tightness In Lower Abdomen And Headache?

hi my mom has been having a weird feeling in her lower stomach kind of by her pelvic bone and she saying that tight that a tightness or pulling sensation comes and goes and she s been having headaches she missed her period And she took a pregnancy test but it said negative & she said she s been having to go back-and-forth to the bathroom. she also experiences most of the symptoms at night whenever she s laying down she said she feels the tightness in the pulling and like a twisting sensation and her lower stomach also feels heavy.