When to take a pregnancy test with a period like mine?

I am on a birth control that allows me to only have a period at the end of every three months. I do not take it at the EXACT same time every night, but around the same time. (Whenever I go to bed whether it's 1, 2, or 3am.) I have continued to spot, but not badly just when I wipe there is residue. My boyfriend ejaculated in me tonight and even though I am on bc, since I have been BARELY spotting and not on the exact same time but very close should i be worried? If so, when do you take a pregnancy test with a period like mine? I don't even know if you could consider mine to be one.