Help?

On the 20th of June, the day after my period, I had unprotected sex with my *then* boyfriend, though I have been on birth control for over a month. Soon after I started becoming nauseous every day…it was a daily thing and I also have become sluggish, dizzy, my head hurts, and exhausted even when I haven’t exerted myself. So, thinking that it was my birth control, I stopped taking it. Four days later, I am still nauseous through out the day and cannot keep *anything* down. Earlier today I spotted…I want to know if I could be pregnant? And why would these symptoms show up so quickly? And what about the spotting?