Insecure and needy boys get dumped just as fast as insecure and needy girls. Imagine your girlfriend asking you about your sexual past. She wants to know what you did to where, why, and when. Do you think telling her these things is going to make her fall in love with you more? Even if you've been chaste its not appropriate to ask.
Now think about what you're doing. You're asking her for information that is likely to sabotage your feelings for her. Are you sure you don't subconsciously want to break up with her or something?
Stop bugging her about it. She is YOUR girlfriend now, and if you do a good of job of keeping her attracted to you, she'll stay your girlfriend. It's important to let your partner know if you have any STDs but there's no reason either one should be asking the other how many people they've fucked.