As mentioned above the adrenaline is a naturual decongestant so for cold / sinus problems, GO for it! If you have a fever, I personally would not ride. The fever is signalling that your body is trying to fight off an infection.
I also take 500 mg of Vitamin C every day. When I start to feel sick, I take my 500 as usual in the morning and follow it up with another 2 tabs (1000 mg) in the evening before bed. This has rarely failed me. I have to be on the death bed when that doesn't work.
Just a tip, don't use antibacterial soaps. These kill "good" bacteria which help strengthen your immune system. I am not suggesting licking door knobs or pay phones, just don't overkill on the antibacterial crap.