Well, the short answer is that yes, you could be pregnant because anytime you have sex there's a possibility of becoming pregnant.
Now for the long answer - since you don't know exactly when your period is due, it's hard to know for sure if the timing between you and your boyfriend was near your ovulation (when you're fertile for conception) or not. Some things to keep in mind about cramps is that they're not uncommon in the week before your period or the week that you're due to ovulate, which is generally about two weeks before the start of your next period.
If you want to know for sure if you're pregnant, I will buy a First Response Early Result pregnancy test. I like these the best for testing when you're unsure of when your period is due because they're sensitive and can detect pregnancy hormones pretty early on, plus the pink dye makes the lines easier to interpret. I would take one at the end of this week when you think your period could be due. If it's negative hold off on taking another one until next week which you also mentioned could be when your period is due to start. This way, if you are pregnant, you're covering the period until your next period is due.
If it turns out that you're not pregnant this time around, but you'd like to start trying, I will invest in an Ovulation Prediction Kit (OPK). It works a lot like a pregnancy test; only it'll let you know when you're ovulating and therefore fertile to conceive a baby so that you can time your sex around it.