When is the best time of the day to take a pregnancy test?

I am on a birth control pill low Loestrin Fe, I never know if I'm going to have a period or not with this pill I have been on it for seven months. However I have not had a period at all the past three months. I'm going to take a test just because I have noticed that my boobs are sore. I have no other symptoms. I'm just not sure with this pill being very sporadic. I had to little girls ages six and two. I do want to third baby however I would like to wait one more year before I start trying...