When is a good time to take a pregnancy test

Hi and I'm new to this really excited and anxious at the same time. We'll so here it goes I'm 3 months late have many symptoms, nauseous, short tempered, emotional been eating wierd cravings but the thing is everytime I take a test it says negative but my stomach feels firm and my bra size gets bigger so is it because I'm taking it at the wrong time of day or could it be stress