Your symptoms are an almost textbook-perfect description of a vaginal yeast infection. Contrary to popular assumptions, the main symptoms of yeast infection aren't discharge or odor, but itching. The irritation usually is exactly as you describe, "both inside and outside" and redness of the tissues--without visible open sores--also is typical. The timing of onsent probably is coincidental with your sexual experience, although yeast sometimes may be acquired from a partner's hands or genitals. Herpes is a possibility and can occur from non-penetrating genital contact, but I doubt that's the problem.
In any case, your symptoms are only a clue; you need to see a health care provider for proper examination and diagnosis. Please do not be tempted to buy one of the over-the-counter yeast treatments. That may be OK once yeast is confirmed, if it recurs in the future--but not for the first infection.
If you don't have a regular doctor or don't want your parents or their health insurance to be involved, call your local health department about a public health STD or family planning clinic; or try a local Planned Parenthood clinic. The charges will be minimal, perhaps nothing.
Good luck-- HHH, MD