I have hives, chills and slight fever (99.5), what can this be?

Fever: A temperature of 99.5 F is not fever, although the time of day your temp is taken might be relevant. Hives are often a manifestation of an allergic reaction to something, although can also be seen in a variety of illnesses. Sounds as if you need to be seen by a doctor and evaluated if this continues. Best wishes.

Many things but: points to an infection which is often viral. If problem worsens or persists beyond 10 days, see doctor.