Hi, I Am Taking Zyrtec Antihistamine For A Hive Like

Hi, I am taking Zyrtec antihistamine for a hive like rash I have. The bottle I have says a 10mg dosage in a 24 hour period. It sure doesn't seem like a lot. I do well but I start itching at the end of the day and wish I could take more. My question is what's a safe dosage I can take in a 24 hour period. It looks like the rash is slowing going away but I want to take it for a while yet. Thank you!