Pregnancy test help

Jacquelyn
So Pregnancy tests say that they're supposed to be taken on the day of that missed period, but I haven't had my period the past two months. 
I'm on birth control but my body has been acting way weird. More hot flashes, crazy food cravings, cramps, etc. 
Does it really matter when I take the test if I'm already late? Or is my body just acting funky for other reasons?