Not sure on pregnancy

I m 29 yrs and had not my periods till yet.Last month it was on 17 July..it’s almost 8 days over in August and had not till yet.I had taken a preg test but it was negative ..should i wait for 3-4 days more..also let me know what’s the right time to do the test…i m totally confused..because m getting bit of pain in my lower abdomne area..it seems like period ay get start any moment.
Please help me out.