How did my optician screw up my prescription?

I got glasses when i was 13, im 19 now and the ones i just got are so different from any of my previous ones its scary. i am nearsighted slightly in my right eye and severely in my left eye, the glasses i recently purchased seem to make everything wobbly and very very blurry. I have used the same optician since i was 10, so i don't want to change offices. should i were my old glasses or try to get used to the weird ones? and also i have been told i was both near sighted and farsighted in my left eye?? whats up with that?