Allergies do not produce fever and rarely body aches, with the exception of sinus pressure.

Never mix medications that have pain relievers in them with another pain reliever.

Have you taken him to the doctor for his allergies? What symptoms did he have before he started medication? If zyrtec has been prescribed for him by the doctor and is not enough, it may not be just allergies he is experiencing or he needs a different type of medication for relief. Do not mix Benedryl with Zrytec: both allergy medications combined might not be the best thing, just as mixing pain relief meds is not a good idea.

A 101 temp is a low grade fever, and usually nothing to worry about.

I have just found out today, that you can give motrin and benadryl to your child, it just cannot be at the same exact time.
My 5 yr old son has a bad cold, and since i found out they pulled alot of childrens meds from shelfs that have cough and runny nose releif in them, i asked if i can give my son benadryle and motrin. I give motrin(2 1/2 tbls) if there is the fever then i was told to wait a couple hours before giving a min. dose of benadryl (1 chewable tablet) only if needed (for cough and stuffy nose before bed) hope this helps you in any way, it was my sons dr who gave me this advise. I would advice EVERYONE to pls call you dr first before giving your kids any mixture of meds, only cause every kid is different and you never know how they will react.