When posting, please try to use correct spelling and grammar so that your posts are easier to understand.
First of all, pre-ejaculate can contain sperm, so it definitely can get you pregnant. There's no percentage that we can give you to compare the pregnancy risk between semen and pre-ejaculate, but we have a handy risk assessment chart here: What's The Risk? - Five Easy Pregnancy Risk Assessment Flow Charts
It may take a few years for your cycle to start being more regular, and you're right about stress and other factors leading to irregular periods.
There are *no* signs (vomiting, headaches, whatever) of pregnancy except for a pregnancy test.
Pregnancy tests are not effective until 10 days after unprotected sexual activity or the first day of your missed period.
Since you have a lot of questions, I recommend reading Am I pregnant?) thorougly and carefully. It should answer most of your questions, and if you want more information, you can post again.