You'll want to see a neurologist, and an infectious disease specialist. Children who are prone to febrile seizures generally grow out of this by the time they're 8. It's not so common for adults to get them, but it's not unheard of either. If you're getting febrile seizures frequently, you need to address why you're getting fevers of unknown origin and figure out why you're immunosupressed. You also should see you're primary care physician so he can coordinate with the other doctors you need to see, as well as run some blood tests, including one for HIV.
Neurologists are the kind of physicians who are specially trained to handle febrile seizures. Neurologists are trained in pathology and immunology. Some of them further their studies to practice pediatrics, oncology, epilepsy and psychiatry units.