I can help you out on one thing: you can eliminate the worry about STDs and pregnancy by just not having sex. I know that sounds hard, but it's worth abstaining if your life is ruined by constant worry about what you will get from a few minutes of pleasure.
Visit your doctor for a yearly well-exam.
Breast cancer is something that can be avoided by yearly mammograms when you are post-menopausal. If you are still of a child-bearing age, then you can so self-breast exams to make sure that you are in top shape. The best way to avoid cancer is to keep a healthy diet and use natural items and eat natural foods.
Enjoy your life and don't worry about "catching" things. As long as you are taking control of your life with wise choices, there isn't anything to worry about
You're probably a hypocondriac like me. Don't do this to yourself. it's not healthy. Maybe something happend in your life to make you worry constantly about your health, but if you take very good care of yourself, you'll heal from anything! Except maybe the major injuries and illnesses, and even then, unless your death was instant or totally uncurable, the body has a tendency to heal itself, my dad says. So stay calm and don't worry, be brave. the more you worry, the worse it will be for you. If you need or want reassurance, try talking to a doctor for your symptoms. It could all be in your head or maybe it could be something else, but in the meantime, it's counter productive to your life, to worry so much. It's not only unhealthy for yourself (heart disease, high blood pressure, depression symptoms), it can make you look older too! So take it from me, someone who's been there, done that. there's really no use in always wondering: "what could this be? ...Do I have [insert injured part, disease or etc. here]?"
Part of dealing with life and it's problems is solving them, and worrying about it, may only be the first step but it certainly doesn't solve the problem. It's like getting help for an addiction, the first step is always realizing that you have a problem and you want to solve it. Good luck and I hope you recover from whatever ailment, physical, emotion or mental, in nature.
I experience the same thing. Since October last year, I felt like I am ill all the time. Its like i put my life intoa microscope and every single little thing I feel becomes a HUG thing and scares the sh*t out of me to the bpopint taht I tremble in fear and I feel like breaking down and cry. My work requries meet to meet clients regualrly so just having a brave face everytime is a constant struggle.