HELPPPPPPP 😫

I'm 15 and I feel pleasure touching my clit in fast circular motions. I've never tried penetration because I'm scared it will hurt. I use my saliva as a lube and I get really wet after a while. After touching my clit for like 10-15 seconds, I stop because my clit starts to hurt really badly if I touch it anymore and my legs shake. Is there a reason why I can't go any longer?