How do I know if my tongue piercing is infected?

If it's sore, swollen, red or oozing pus. If it's been pierced for some time, take the bar out and clean it, rinse your mouth with warm salt water or get some tea tree oil and add 5 drops to 1/4c water and rinse with that.

If its infected, you need to go to the doctor. There are products out there that will MASK the symptoms of the infection, but not fully cure it. Infections need antibiotics -- period.

Symptoms of infection are just as flossie said, but an advanced infection can also include fever and/or chills.