If I took a pregnancy test and the result appeared negative, however...?

It appeared negative. The control line showed up, and a pink line showed up as negative, however there was a very faint pale grey line that could've been a cross to be positive, so I was just slightly confused. I took it as being negative. But after watching that show "I didn't know I was pregnant" got me just a little nervous lol. I've been very tired, lethargic, my abdomen gets kind of crampy for no reason. I'm past the period (which came late and was a little strange). I take birth control pills, but I was a day late starting the last pack. What do you think?