Firstly, if you insist on having sex at a young age then make sure you're protected (condoms/pill both etc...). Trying not to lecturebut it's exceptionally irresponsible for anyone to be having unprotected sex (unless ttc/not minding should pregnancy happen).
Buy yourself a hpt, since it's been over a month since you had a period then it will most likely show up positive if you are pregnant. Symptoms of pregnancy vary from woman to woman but skipping periods is usually a pretty big indicator (although not all women stop af they're in the minority).