My Gf is freaking out thinking that she is pregnant?

she had a period 3 days after we had but now she is freaking out becouse she hasnt had it in almost a month maybe 2. She refuses to go to the Genotoligest becouse she is scared(she is under age =/) so she has nvr been and im just wondering if there is sum way to get her to go. im worried about her she is stressing out about it and i know that if remales stress it will even more delay. im not sure what to do can someone help and give me some advice. THX