Basically you'll want to avoid high fat foods and also foods that are slow to digest, such as red meat. Those are the ones that will stimulate more acid production and for longer periods of time. The earlier in the day you are eating out, the more you can indulge in hard to digest foods. You want your stomach to be as empty as possible by bedtime. The junk you were accustomed to eating on a daily basis, like pizza, hamburgers, etc., you should now eat only as occasional treats and not staple foods. It's different for each person, but I try to eat more carbs, fruits, vegetables, eggs, nuts, etc., and less meat and fried greasy stuff.
Some people have trigger foods that cause their LES valve to relax and make their reflux worse. My valve never closes so those trigger foods don't matter to me. If you have an endoscopy done, your doctor should be able to tell you if your valve is always open or not. Since my reflux is always on, I focus on eating foods that cause the stomach to generate less acid for shorter lengths of time.
Like you I went for a long time getting sore throats, stuffy nose, etc. which I always thought were head colds. I figured I had a defective immune system to be getting so many colds that lasted for weeks and sometimes months. I also wondered if I had allergies but I never tested as allergic to anything and taking allergy medication never helped. Now I know it was always reflux. I didn't believe I had reflux until finally I had an endoscopy done and the doctor put the picture under my nose showing the obvious acid damage to the lining of my esophagus. Then there was no denying it. Now that I'm on PPI's, I never get "colds" anymore. If the PPI's are relieving your "allergy" symptoms, then odds are you don't have an allergy and probably it's reflux.