firstly to buy a pendulum or any crystal for that matter, close your eyes take a deep breath and calm yourself. then very gently lift the crystal asking if it belongs to you. if the crystal is right for you it will lift easily and if it is not you will find a resistance like it is being pulled to the ground.
now for all the problems you have listed here are the crystals that will help.
metal toxic - smokey quartz
candida - carnelian
immune system - bloodstone ( will also look after the pre diabeties)
digestive - a combination of jasper and citrine
osteoporosis - amazonite
here are some of the crystals. if you would like more details please log on to my web site and there is a free healing required button please feed in all the details there and i will give you a detailed reply.
Dr. Seema Anand http://www.lookbeyondindia.com