Infections take a lot out of the body, whether you are dealing with a parasite is largely unknown. Nausea could be a tell tale sign that there is something in the gut triggering an immune reaction. Other possibilities are yeast or some rogue bacteria.
Infections draw resources out of the body and fatigue and stress are good signs of infection.
Magnesium loss occurs with activation and magnesium is vital for many function, particularly energy production. Tension headaches can be caused by mag loss.
Infections also create a high oxidation state in the body and this oxidation causes damage in the body.