SLE patient. Everything I read about lupus says that gamma globulins are high in lupus. However, my AgG and AgA are actually fairly low? Explanation?

Specific ab. It is not the total quantities of you immunoglobulins (IgA, IgM, IgG, IgE, IgD ) that count but the specific activity of the antibodies which define your body's immune response. If your Ig G and IgA are low, you likely have a problem with immunodeficiency. I believe an allergy/immunology consult may benefit you.
Immunosuppression. Could be the cause, due to the drugs you are on to control the SLE, I trust you follow common rules as avoiding people with respiratory infections, crowded/congested places, etc.., take care.