In addition to all the excellent advice given by so many other people you could also try an enema or a colonic. I feel that we often fall ill, when our body needs cleansing. So these two treatments can give immediate relief.
You could also try taking some raw manuka honey in warm water to boost your immune system and ease the sore throat.
I find gargling with warm/hot (as hot as you can bear) with a drop of some essential oil that you like (i like tea tree at the beginning of the day and maybe lemon towards the evening), ver soothing for a sore throat and the essential oils help fight the infection as well.
Another reason we can fall ill is when we have been pushing our body hard and the body is asking us to slow down. So in this case I find receiving a Reiki treatment to be very beneficial.
For building immunity over long term, I have found Reiki to be the most effective for myself. I learnt Reiki 10 years ago. I have been giving myself a Reiki treatment everyday. Over the years I find that I do not fall ill as often as I used to. When I do fall ill, I find that I recover quite quickly.
Everytime I am feeling unwell, I receive a Reiki treatment from someone else and it always help.
If you would like to find out about receiving a Reiki treatment or learning Reiki please visit my website on http://www.reikiwithmamta.com/