You Are Not Alone, But Almost - But that's really another story, though an important one. If you are Type O though, you'll either have Type O positive blood or Type O negative blood. If you have Type O negative blood, the good news is, any one else can use it. As noted above, you are the "universal donor". The down side of it is, and it's a rather big down side, you as a Type O negative, can only use blood from another Type O negative person. Somewhat of a bummer. To make matters a bit worse, Type O negative blood is not among the most common of blood types, Type O positive is. In most countries, 2/3 or more of the population have either O + or A + blood types. Those having negative blood types make up about 12 or 13 %, with about half, or 6% being O negative. If you need a transfusion of O negative blood, your best bet is New Zealand or Spain where 9 to 105 of the population is O negative. In China you'd have a tougher time of it, as less than 1% of the Chinese population would test O negative.
These numbers may not mean too much, as hospitals in most major cities in the world do all they can to keep an adequate supply of the various blood types on hand. You could conceivably find yourself in trouble however if, being a Type O negative individual, you required an emergency blood transfusion in a remote part of China. You would certainly be looked upon as a valuable resource however! For the most part, there will probably be access to the type of blood you need, and if you do need blood, the first thing that will be done is to measure your blood type to see what you can accept. In the United States blood reserves and blood transfusions are regulated by the FDA, and despite an occasional scare story, the process is quite thorough and safe. Blood is not only stored in accordance to type, but also is screened to make certain that there are no dangerous pathogens (hepatitis, HIV, etc.).
Plasma Is A different Story - There is some good news however. If you have Type O negative blood and it is only blood plasma you require, you can use plasma from any of the other blood types. The plasma does not contain the A and B antigens that Type O blood would normally create antibodies against. The antigens are associated with the blood cells and not with the plasma, the liquid part of your blood. Conversely, your plasma could only be used by another Type O (positive or negative) person.
If you don't know your blood type and want to find out, you can either submit to a blood test, quite a simple thing, or donate blood. In either case your blood type will be documented and you'll be informed as to what it is. Your blood will also be tested prior to surgery or if you are going to donate or receive an organ. Women who are planning to become pregnant or have become pregnant should have their blood tested, and in some areas blood test are occasionally taken to see if two people are close blood relations.
A Visit With A Vampire - Blood samples are normally taken from a vein in your arm, usually just above the inner elbow. You may feel a prick when the needle is inserted, but more often than not you may not feel anything at all and certainly no real pain. The person drawing your blood is called a phlebotomist, and a good one takes pride in taking your blood without your feeling anything (sort of like a vampire), and leaving no marks or bruises. You don't have to go through fasting or anything like that to have your blood type determined, and unless you are taking blood thinning medicine or have clotting problems, the test will cause little or no bleeding when the needle is withdrawn. You do need to let those drawing your blood what medications you are taking, or if you have cancer or leukemia as any of these could cause a false result, particularly in establishing if you're positive or negative.
So, your blood test indicates you have Type O negative blood. You are in a minority, but in most countries in the world you will have plenty of company, so don't let it worry you.