Help what's this pain

Im 17 w 2 d. I have the worse back pains sometimes to the point where I can't walk or anything. It is so bad that one time I got this pain at the store and I couldn't take another step I started screaming and crying with pain plus I had to pee so bad so since no one could move me I seriously had to pee my pants. But that I think I need to tell my doctor cuz the pain is so unbearable. Any ideas what this might be? I'm 18 I don't think I should be having serious back problems.