Could I be pregnant? Possibility or paranoia?

Okay well I had unprotected sex at the end of April a couple of times. And I got my period a few days later. Then again in May. Although it oddly was short, like a few days when it is normally seven. And this month I am a few days late. And I've been tracking my period for a while now and the calculation is on spot each month, sometimes a couple of days earlier than usual. But I have never had a late period. And this month my stress level, diet, exercise has all been the same. Then I've heard women can get their period while pregnant so it kind of makes me wonder? It's just so weird because it has never been late. And I didn't notice any PMS symptoms either, but I'm sure I'm just being paranoid. I wonder why it is late. Any advice?