I'm 19 years old and now 20 days late for my period. I've take 4 test And all have been negative. What should I do. Could I be pregnet or could it be that I started college and a new job?

Could be anything. Be sure you're taking the tests using first morning urine. It's not uncommon to have false negative results. All you can do now is see if you start your next period and if not, test again. But many things can cause a missed period.

What are the timespans between your tests? If you're very concerned about a pregnancy you should definitely make an appointment with your gynecologist to take a blood test. You will most likely get the results the next day and they are extremely accurate.

20 days is enough to get right result that said negative. You should consult with gynaecologist.