40 days since period ttc no sign of period feel sick and bad back ache keep feeling damp scared to do test incase it's negative?

Fear is bad. Fear is never healthy, if it's avoidable, pregnant or not. Do the test! Once you know you can move on and deal with the pregnancy or lack of it properly. Follow the instructions on the box exactly. Repeat in a week. If no period yet, see doc. If you are pregnant you need to know to start taking proper care of you and the baby to come!