I took three pregnancy tests last week, all negative

I took three pregnancy tests last week, all negative. I missed my period yesterday and told my fiance that I might be pregnant, but probably just late. He went to the store at 5 AM for stuff for work and came home with a package of pregnancy tests and a cup of coffee for me. I took a few sips of coffee and said, "Okay, let's go do this" thinking it would definitely come back negative. I saw the control lines appear and then a minute later the other faint line appeared! I was shaking in shock! I came back to our room and asked him if he wanted to see the results, as I have in the past, and then showed him the test. I still can't believe it! This is our third child combined (one each from a previous relationship), second month trying, and first child together!