Active Ingredient of Coldec

What is the active ingredient(s) in Coldec? I have severe allergies that seem to be indoor (I think it's to dust), when I go outside they seem to clear up. The Coldec was the best allergy medicine I've ever been prescribed vs. Claritin, Allegra and Flonaze. I have taken several over-the-counter allergy meds also (including Tylenol Severe Allergy, and OTC Claritin)and NONE of them worked like Coldec. Clarinex worked ok too, however Coldec was the only one that cleared up ALL of my symptoms. My doc took me off of them though because I have Tachycardia and they thought the allergy meds may be causing it. After removing my meds and realizing that my symptoms had not improved, they put me on Allergra 180 which didn't do a darn thing for my allergies. One day I was experiencing severe allergies (non-stop sneezing, itchy watery eyes, itchy throat and a very runny nose). I took an Allegra 180 and 4 hours later, it seemed my allergies had gotten more worse than better. Finally, I was fed up and had enough. I still had a Coldec tablet left so I took that and like 30-45 mins later, ALL of my symptoms were completely GONE. All I want to know is, what is the difference? Why does one allergy medicine work and not the other? What is the Active ingredient and mg in Coldec vs. the Allegra 180? I don't remember the dosage of the Coldec though, but it was a dark purple oval shaped tablet.

Please get back to me on this when you get a chance. Thank you for your time.

Melissa