Could someone help me please

My fiancé and I have been trying to concieve a baby for over a year now and still nothing but my peroid is 3 weeks late today and I've taken atleast 4 pregnancy test and they still all show up negative. I haven't had any bleeding, but I have felt nauseas and tired lately, but I also just got over being sick with strep so that could be why I'm tired. Should I just wait a couple more days-week to see if it changes or should I go to the doctors and see if anything is wrong?