you're asking like a bajillion things at once, but i'll try to take it bit by bit.
first up, either you misunderstood your mom, or she misunderstood her coworker. sperm do not automatically die when exposed to oxygen. however, they do die when they dry out. if there's moisture around, they can live for a while.
As for how do you know if you've had an orgasm, please read the following: Sexual Response and Orgasm ? A User?s Guide
Should you feel ashamed for what you did? Well, I'm not going to tell you what to feel. Do you feel ashamed? Then you need to reckon with your own emotions and sort out whether you are ready to be sexually active (yes, *you* are sexually active), and hold off till you really are ready. However, if you're fine with what you did, then as long as you are totally responsible for your actions and take the proper precautions, then you should be fine.
As for "pregnancy symptoms," don't rely on those because they're *so vague* (btw, read that link i put up). Instead, wait 10-14 days following the incident, of the first day you miss your period and take a home pregnancy test. Fromwhat you said, it sounds like your risk is low to nil. For more on preg risks, read this: What's The Risk? - Five Easy Pregnancy Risk Assessment Flow Charts
also, more reading for you:Safe, Sound & Sexy ? A Safer Sex How-To
Summertime, and the living's easy...