Dear Aneliajudd, hello
Whenever you fall, your hands stretch as a reflex. So when you had a fall, your hands must have stretched as a measure to balance your body and prevent your fall. Therfore your shoulder got sprained.
You should take pain killer along with muscle relaxant
for relief after consulting your Orthopedician.
Also have X-Ray of your left shoulder AP and Lateral view.
I hope this is helpful to you. Thanks.