Lost my virginity, now my period is late

I lost my virginity to my wonderful boyfriend last Sunday, I don't regret it all. We didn't use a condom and I'm not on the pill, but he did pull out. Monday I left on a cruise for Mexico, and Tuesday - the day my period was due - I had light brown discharge and light pink spotting, but no period after that. I still haven't gotten my period, which is very unusual because my cycle is pretty regulated. I'm cramping and my back is aching, and my boobs are definitely bigger... When should I take a pregnancy test????