I'm a healthy 28 year old with a generally regular cycle. I was just married, and had sex for the first time on the 8th. It's now the 14th and AF is four days late. I had some brown spotting yesterday, and nothing today, but the last few days I've been urinating more frequently and sleeping a bit more, and I woke up early this morning nauseous and with lower back pain. Is there any chance at all that I could be pregnant? If so, when would I be able to test? And if not, what could throw off my usually regular cycle so much?