Cooking the fruit definitely helps because it breaks down some of the enzymes. We haven't tried freezing it but that sounds like a good idea!
I'd also suggest continuing to take an antihistamine daily until your allergies are under control. Singulair works completely different from antihistamines and should not replace an antihistamine. If zyrtec causes drowsiness and your insurance will cover it, I highly recommend allegra 180. There's also a newer antihistamine (RX) only called xyzal. I haven't tried it but am considering asking about it or liquid allegra for my DD. I am not sure but think that xyzal is a more effective form of zyrtec with less side effects (like claritin and clarinex are similiar).
Rhinocort is a weaker nasal steroid spray. My children use nasonex. Nasocort AQ is suppose to be good, as is veramyst. Both are considered the *strongest* nasal steroid sprays.
We have the plastic, zippered covers on our queen sized mattress and boxsprings. I've had them a few years but will see if I can figure out where we got them from. Also, some of the online allergy stores carry allergen powders for the carpet that are stronger than the grocery store types. I've not tried them though so don't know how good they are.
Last thing, it's really not uncommon to need a combo of allergy meds. My DD is currently on zyrtec, nasonex, astelin, singulair, & zatidor and is still miserable (hence wanting to switch her to xyzal or allegra.) She is on allergy shots (started at age 2 and is 8 now). They've helped immensely with her asthma and improved her enviro allergies, too; however, she still struggles during the worst part of the allergy season.