Need advice please!

So my last period was on the 23rd last month and they always come near the end and they never run into the following month. It's the 27th now and I still haven't gotten it. Doesn't even feel like it normally does right before I start. I took a test the day before yesterday and it was negative but the way we have been having sex could very well point to positive. Should I wait a few days and take another? Has this personally happened to anyone on here who has been pregnant before?