Period 5 days late, negitive hpt

My period is 5 days late which has never happened. I've been experiencing extreme tiredness for about 3 weeks. I've had flu like symptoms for a week. My lower back is achy and I barly have an apitite these days and I'm running in and out of the toilet like there's no tomorrow. On the 19th of jan I had what I assumed to be a period which lasted for 2-3 days(normal my period is 4-5 days) and my boobs where very tender before hand which isn't a pms symptom I normally have. I've taken a test which was negitive but I feel that it was wrong. Could I still be pregnant even with a negitive?