Blood on toilet paper can be due to many reasons. But as you mentioned noticing blood after urination, it is most likely from urinary tract or reproductive tract. Streaks of blood on toilet paper can be noticed due to anal fissures or hemorrhoids, but these are highly unlikely in your case.
Without any other symptoms you need not worry as it may resolve if it is due to dry vagina or mild break through bleeding. This can be common if you are using birth control pills and there is nothing to worry. Dry vaginal area can be a source of mild bleeding when you wipe with toilet paper. Urinary tract infections (UTI) are common in young females and can present as painful urination followed by streaks of blood. Fever and frequent urination can be present in UTI. If you are having any of these symptoms, you need to take an antibiotic course. Kidney or ureter stones can cause bleeding from urinary tract. Renal stones usually associated with flank pain and difficulty in urination.
If bleeding does not resolve on its own and if you are having any other symptoms, you may have to consult a general physician for evaluation and further referral to urologist or gynecologist based on the cause of bleeding.
Hope this helps. Thank you