Hi Matt, welcome to Healingwell
I will answer your questions the best I can.
1. Like lerie said, allergies play havoc on your immune system. Once your immune system is lowered, you are prone to more sensitivities. If allergies have been with you for a long time and you do nothing for them, it wears you down after a while because think of it this way....allergens are an invader to your body, your body thinks it has to go into overdrive to get rid of it. If nothing is done for your allergies, your immune system needs to comepensate so you may feel ill all the time.
2. I found out that even if my states pollen count is low, I still have a high sensitivity to ANY pollen in the air. Listen to your body and not the forecasts.
3. Our bodies natural temps can range from 97 to 100, it flunctuates. If you are feeling like you have a fever, you may very well have a mild infection. Fevers are your body's way of fighting off invaders. Keep an eye on it and if it becomes worse, definately go to the docs.
4. I have never had allergy shots but my hubby's aunt has severe allergies and it took almost a year for her to see a difference. It does take a while and sometimes even then it may not help. So this is one of those let wait and see kind of things.