Advice please

My period was due on Sunday 18th September but still hasn't arrived. I've been sick most days at the same time(could be a coincidence) and have been having bad pains in lower back, headache and dizziness. Took a test yesterday afternoon as was driving myself mad and it came back negative- not sure whether to wait another week or so or book an appointment with the doctor? We've not been trying for long but I'm worried something is up with me as my periods are normally really regular x