I’m pregnant from precum

Me and my boyfriend have been using the withdrawal method since we got together a few months ago. He’s NEVER came inside of me. I’ve always heard it’s a very very small chance of getting pregnant off of precum, so I didn’t even worry. Well at my checkup with my gyno, the pregnancy test came back positive. I’m so worried! I’m only 18 , and I already have a 9 month old from my previous relationship. Has anyone else on here got pregnant from pre cum??