Is there any way to test a (young) girls fertility?

I don't know if being 13 has anything to do with it but i do get my period but i might have left a tampon in (ewww i know) but i swear its not there but if i did have tss (nope) or if i had it for a second but then it went away then am i still fertile, i have had my period for almost a year and it hasn't come since february 28th-march 3rd. Am i a total dummie cuz i don't know any of this or is it just a part of learning it all?