0 positive or negative

By getting a blood test! How else can you determine whether your blood is o positive or o negative? You can't do it yourself so you have to go to a clinic that runs tests and you will be able to get a report from them in a day or two. So you will know exactly where you stand and blood tests are not that expensive as well. Other than that I can't think of any other way that you can check whether you blood is o positive or negative. if you are scares of needles then you will never find out. 

Ask your doctor. If your doctor already has your blood type on file, then you need not do more than ask!
Donate blood. When you go in, ask the staff if they can tell you your blood type when you're done. However, they typically won't be able to tell you right away, because of processing as the unit of blood (or the specific component -- red blood cells, plasma, platelets) needs to undergo several tests first.