What's going on with my teeth? Why are they moving? I don't understand why. (photos)

two years with braces and thousands of dollars later on my teeth I now have my braces off.I wear my retainer every night as directed and sometimes during the day because I'm scared that my teeth will be crooked again. I had to have a molar pulled on the bottom and also wisdom teeth removed but now my teeth are shifting! I do not want braces again. My two front teeth are overlapping eachother once again even with a bondage permanent. My bottom teeth are crowding again as well what do I do!

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