My son has temp of 39.1 he is two, has had pneumonia 2 weeks ago one side of face and eye are very red. What could be wrong?

Possible cellulitis. If there is fever and only one side of the face is red, it is possible that he has cellulitis, a bacterial infection of the tissues of the face. My best recommendation is that he be seen by his pediatrician, and with the height of the temperature, i would recommend that he be seen today.