Since you used a condom. The chances are lower...
You said its your first time having sex. I assume you were a virgin?
If so, usually to some females, after one losing her virginity her hormones change and it is absolutely normal.
If it is not your first time, this can simply br a little delay caused by many many factors. Such as , physical activity and stress and lifestyle.. Etc.
Keep me posted
There is a chance that you could be pregnant, but the fact that you used a condom does reduce that risk. If your period is due and hasn't arrived- take a test to be certain. Late periods can be caused by a lot of things, pregnancy is just one of them- medications, stress, illness, or even just changes in your environment can get you a little off on your cycle.