How Many Pills Can I Safely Take In 24 Hours?

How many pills can I safely take in 24 hours? I am a woman, weighing 114 pounds, am 79 years old with no known kidney disease and in fairly good health. I have been taking the Allegra tablets, 2 pills a day with fomotidine 20 mg since September 2, 2016 for large hives which my allergist can't explain. I didn't have any hives for most of Dec but then they came back.