Im only 15 and my back has been hurting after my bike broke under me. did i hurt it bad?

at least a week ago i was riding my bike with my mom when suddenly the chain on my bike broke under me and stopped automatically. i flung forward and straddled the bar(ouch! thank god im a girl xD). then jolted back and hit my lower back on the seat. even though i didnt see a bruise it felt like i had one and its been hurting ever since. im only 15 so this shouldnt happen. ive also been trying to become as flexible as i was when i did gymnastics years ago so ive been doing back bends and front walkovers could this be a problem too? did i hurt it bad? i only want to see the doctor if its necessary(im about to go on a very expensive trip and i dont want to waste any money that my parents need).