it is very unlikely that you are pregnant - don't worry about it because stress will only make you get more stressed out about it - don't worry, your body is working fine!!
It is not possible to get pregnant with precum or semen on the finger, unless large amounts were deliberately inserted into the vagina and touched the cervix.
Unprotected, penetrative vaginal sex is needed to cause a pregnancy, usually around the fertile days.
There many reasons women miss their periods that aren't pregnancy related. Stress is one of them. Why don;t you take a home pregnancy test to rule out pregnancy? wish u the best!