It does sound like a yeast infection again. They generally swab for it if you went to the doctor and at that time, they look to see what else might be in the discharge. So, if you were told you had yeast at your doctor's appointment, I'd say it's just yeast. And it sounds like it is recurring. But no one can diagnose you from here. If you want a definite answer, see your doctor.
I would NOT have unprotected sex though hon. That's an std or pregnancy waiting to happen. Very unwise as I'm sure at 15, a pregnancy or std would be pretty unwelcome. Buy some condoms and use them every single time.
You should just go to doctor