Could i be pregnant? :(?

okay yes i know i'm young.. me and my boyfriend had un protected sex and no he didn't pull out. I'm not hear to get a lecture about, how we should of used a condoms! I'm here for advice and some answers. Well friday we had sex, and during then i started my new pack of birth control pills.. i was on my fourth day. Anyways today i have cramps and feel slightly nauseous. I'm wondering if pregnancy signs can show up that early? It's to late for plan B and i feel like waiting a few more weeks to see if i don't get my period; feels like such an eternity!! how soon can you know?