Injured Lower Back from Kettlebell Swings

So yesterday I started back up with the full kettle bell workout I've been using: 12 reps Kettlebell Deadlift 12 reps Goblet 12 reps Russian Swings 12 reps Around the World 12 reps American Swings X1 set with 8kg kettle bell and X2 sets with 10kg kettle bell. This morning I tried to turn over in bed and had terrible pain in my left lower back. Trying to get out of bed was even more interesting. If it wasn't for the pain, it would have been quite comical. Searching on the internet, it seems likely to be my form and I think I have pinpointed it to swinging too low. Over the course of my research I have found that I should aim the kettle bell on the down move towards my 'zipper' and also (just in case) on the up, stop at 1 'o'clock just in case I am overextending. Today, I will try to complete my workout using my 6kg kettle bell until I get my form right. The 8kg kettle bell that I used yesterday is far too big for kettle bell swings. The handle is quite...