you might be putting too much stress on your leg
You could be using too much back. Remember, the swing is a hip movement not a back movement. You are probably dropping your chest too low. Try being in a “hike pass” (as in football) with your hands close to your inner thighs to relieve stress on you back.
Probably rounded back instead of arching it. I did that in beginning. Use smaller bell & work up by increasing reps and speed as strengh increases. Take it slow.
My first thought is that you may have started with too much weight. I work with ladies from 12 to 62 with kettlebells, and I made ALL of them start with 10 pounds. You may have someone watch you to see if your FORM is actually correct. Sometimes you think your form is correct, but someone who is trained may see ONE small thing you can tweak to get it just right for your body. Good Luck! Colleen