Dark spots can be an adverse reaction of your skin for all the waxing. I suggest you go easy on the wax or find an alternative to it. Continuing with the waxing can give you a lot more serious problems in the future.
For a natural remedy on dark spots, I suggest you use really mild natural products like oatmeal with honey or little water as a mask. It can help whiten your skin complexion and even out your skin tone.
Hope this helps.