We doctors do not believe that teething
If at all it may cause low grade fever
(less than 100`F), crankiness, night waking, slightly reduced appetite for solid food along with redness and swelling of gums.
Lethargy and high fever
are not seen associated with teething.
Does he have any other symptoms like cold, cough etc? If so he might be having a virus.
What I would suggest is to get your kid seen by a Pediatrician
to rule out other causes of fever.
For easing teething pain, you can give him clean teethers, vegetables like carrot to chew. When you give such vegetables be sure its big enough and does not break off as small pieces may cause choking. Teethers will be safe.
You may also use mouth gels recommended for babies to reduce the pain.
You may also give oral Acetaminophen
in right dose to ease the pain.
Hope you find my answer helpful.