Just get yourself tested right away. There really are no symptoms until later on stages and most people who have hiv, basically look and appear to have the same health as other people. It affects the blood, so it really doesn't show until later on.
From the info I got, it's pretty much, any exchange of body fluids (not including saliva unless there is a cut in their mouth), and unprotected sex, is one of the most common ways. Just be more careful really, is all I can say. Wearing a condom protects you (not 100%) but mostly prevents from some stds, ie. Herpes, chlamydia, etc etc.
If you are really sexually active, then the best way is to use protection. Think about yourself, for once. If you do contract an std or aids, it's really for the rest of your life. All I can say, is be careful and be tested. And if you are positive or negative for it, then this is where you can start to change. Wear a condom, and when you find the right person; one who will treat you right, then you can maybe share unprotected sex with them - (only if the tests are negative). And that's another thing.
But other than that, good luck. And hope you do find something of value in yourself that you don't have to give to other people.