I'm not surprised that it is still red, swollen and tender. Cartilage piercings are one of the hardest piercings to heal, and they are also the slowest to heal as well. With most other piercings, you start feeling better the next day after getting pierced, or the day after that. Cartilage piercings can remain this way for up to 2 weeks before you start feeling better.
Signs of infection include severe redness, severe swelling, and a yellow or green discharge that smells bad. An advanced infection can also include fever and/or chills. What I mean by severe redness is, it would be so red that its actually almost purplish in color. Severe swelling can look like your ear is actually swelling around the jewelry, almost looking like its going to swallow it. If you have any of those symptoms, infection is possible and you should see a doctor.
Remember that a piercing is a wound to your body, and any wound is going to cause some form of swelling and discomfort. If it is taken care of properly, these things that you are experiencing will go away as fast as your body allows them to.