Why allergic medicine like cetrizine make my body ache after eating it?

Never heard before: Not a side effect that I have ever seen/ heard with certrizine. Could be part of a viral infection starting though...

Not a known effect: I cannot find body aches listed as a reported side effect to cetirizine, so it is unlikely that the aches are related. Sometimes viral infections can resemble allergies, and are associated with body aches. Some people do have odd reactions to medications, though; you could try taking it at a time you have no allergic symptoms. If you don't get body aches, then the medicine isn't the reason.

2 reasons: Whatever medications depletes cell energy causes body ache usually a sign of glutathione depletion - that is why our body aches before getting fever the other cause could be acute change in body pH making body more acidic - both can be corrected by taking oral nac supplements and aloe drinks.