Can A Precum Touch Cause Pregnancy?

Hi, im 18 years old and my girlfriend is 16. Weve recently started haveing sex, and weve been using condoms always. The thing im worried about is that she may have touched my precum before we put the condom on, and then after we put it on she still rubs my penis to keep it hard right before we have sex. Im sure that this has happened once or twice. We havent used any extra protection yet, but i recently bought spermicide and were gonna use it next time. We just started this month, and its been 5 days since she was sapposed to get her period and she hasnt. She tells me that its because she started having sex again, and so it gets delayed. She said its happened to her before that when she starts or stops haveing sex abruptly for long periods of time, her period comes late. But im not sure if thats true. Im very worried that she may be pregnant, she hasnt shown any symptoms of getting her period at all (cramps, aching breasts, mood swings, ect.). The only thing that keeps me hoping, is that she only pulled out with her ex boyfriend when they were dating (using no protection), and they did it for 2 years, and she never got pregnant, infact she even missed periods sometimes, but nothing bad ever happened. Should i be worried?!