I'm 18 year old female who is currently sexually active , I took a pregnancy test 5 days before missed period at clinic , it came back negative . I have a period tracker on my phone and lately I have been coming on at the beginning of the month and I would come on a couple days before the months out . My last recent period was August 31- September 5th . My period tracker told me I shouldve came on by now . And it's the last day in sept. but along with this I have been having an argue to vomit , but I haven't , headaches lower back pain and lower right abdomen pains . Could I still have a possibility of begin pregnant ?