My Brother says he doesn't get relief unless he takes H2 blockers in addition to H1 blockers. H2 blockers are meds like Pepcid or Zantac. H1 blockers are Benadryl, Zyrtec, Claritin, etc. My Brother uses Allegra and Zantac for his sinus allergies.
I use Pulmicort suspension for inhalation (Pulmicort Respules - for use in nebulizers) sprayed up my nose to help with congestion. The usual nasal steroid sprays like Nasonex are too weak and don't work for me. Claritin, etc., don't do anything for my sinus congestion. There is also an antihistamine nasal spray called Astelin that may be helpful for you (I got side-effects from it so can't use it).
Yes, food allergies, sinus infections, etc., can contribute to sinus congestion. I find milk/dairy consumption particularly contributory to sinus congestion myself.
Several years ago, I had obvious signs of a sinus infection. I was amazed at how well my sinuses cleared with treatment of the infection, and the clearing lasted for about 6 weeks after finishing the 30 days of antibiotics for the sinus infection...and this was in Spring, right during my worst tree pollen time of the year (birch pollen...causes all sorts of troubles for me).
Another thing to consider is cross-reactivity between pollens and foods. For example, I find if I eat apples during birch pollen season, I get a reaction from the apples. And my Allergist said eating the apple during birch pollen season could cause worstening of my pollen allergy symptoms as well. I'm fine with apples as long as it isn't during tree or grass pollen seasons (both trees & grass cross-react with apples).
A Naturopathic Physician may be able to help with immune system imbalance issues that may be contributing to your allergy symptoms. Also, gastrointestinal dysbiosis (bacterial/yeast imbalance or overgrowth) may contribute to the development of and/or worstening of allergies and may also need treatment.
I hope this helps - take care,
Chronic Lyme Disease, Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, Pancytopenia, chronic malabsorption/malnutrition, etc.; G-Tube; Currently TPN-dependent.
Meds: Zofran, Pulmicort, Heparin (to flush PICC line), IV Ceftazidime (for Pleural Effusion), Colloidal Silver (used topically).