Welcome to HCM
As per your detail information the method you prefer during intercourse it will not give 100% contraception
because during withdrawing if some amount of semen comes out in vagina then it will lead to pregnancy
. As you are just 17 years old your body is not ready to become pregnant . your symptoms showing that you might be pregnant so go for UPT OR CONSULT an gynaecologist , And in future use more assured method for contraception .
Hope I have answered your query. I will be available if you have any further queries.