I'm finding myself in a very similar situation.

My period ended on the seventeenthish, and I had unprotected sex a couple of times that weekend. I've been pretty exhausted and a little queasy for like a week, and for the past fourish days my breasts have been hurting SO much and have seemed a little heavier.

I've been googling like crazy and I know that the breast pain and nausea are early signs, my tiredness too, though you didn't mention it as a symptom for you. I don't know about the discharge. I've been going crazy over it.

The first response tests you can take 5 days before your period is expected, but it is a bit expensive. Good luck figuring things out =-)