Questions about fevers in a teenager are best answered by a pediatrician.
There are many different causes of fevers. However, seasonal allergies typically do not cause fevers. The symptoms of allergies--runny nose, watery eyes, cough, nasal congestion--can also be caused by viral respiratory infections. It is possible for someone who appears to be suffering from a environmental allergies to actually have a viral upper respiratory infection.
Viral upper respiratory infections typically resolve on their own and do not require any specific treatment other than supportive care. However, if a fever
persists or if it is accompanied by any additional symptoms that do not clear after a few days, it is best to consult a physician who can perform a more detailed history and physical exam to make sure that there are not any other underlying medical issues which should be addressed.
Of note, when following a fever it can often be helpful to keep a log of actual temperatures. This can make it easier for a physician to get a sense of how long and how high a patient's fevers have been. A true fever in an otherwise healthy person is considered to be a temperature over 100.5.