[Eternal]

Pregnancy symptoms do not start until about four weeks or more after implantation. So it's likely your tenderness is actually just a sign that your period is about to start. When I was 17, my periods were really irregular, sometimes I wouldn't even have a period each month. If you used a condom and there were no holes, then you very likely are not pregnant. Take it easy because if you stress, it will mess with your cycle even more. After two weeks, you can take a pregnancy test, so if that will help you feel better you can go ahead and take one.
I think you and this guy need to make a plan in case something does happen, though. I also recommend you talk to your mother about getting birth control. She doesn't have to know you are sexually active, birth control can do many things like clear up acne and regulate your period. Having two methods is a really good idea if you are going to be sexually active.