Thank you for consulting.
There is no need for panic. First, you have to understand that penetration need not be all the way and pulling out before ejaculation (coitus interruptus) is not 100% effective especially in inexperienced teens. There is always a chance for some ejaculate to enter into vagina before pulling out. Safe sex with use of condom is always better to prevent becoming pregnant. Pre-cum usually does not contain sperms but it is debatable and one cannot be sure.
Even if sperm entry happened, there is less chance of becoming pregnant if it happened before or after ovulation time which is roughly about 12th day of your cycle or 2 weeks before your periods. The symptoms you are having are non-specific and cannot always be attributed to pregnancy and can occur as part of pre-menstrual syndrome (PMS). Pregnancy tests are the best way to be sure. Urine pregnancy tests are easy and can be done at home. Blood pregnancy tests are more accurate than urine tests but they have to be done in clinics. Both tests measure a hormone called hCG (human gonadotropic hormone) and can be taken as early as 2 weeks after conception. Even after negative tests, if you have a missed period or having any persistent symptoms like nausea, vomiting, morning sickness etc., please consult a gynecologist as ultrosonography can be done to visualize your uterus to rule out pregnancy.
Hope this helps. Do get back to me with any further questions.