Its not uncommon for this to happen, particularly when you change from a cooked food diet to a raw diet.
Usually, it grows until a certain point, and if eliminating the acne-aggravating foods,
the growing will happen at a much slower rate.
Eventually, it will burst, or fade away.
You can use any topical acne treatment to speed up that process.
Pimples can form basically anywhere, but yes, its not common on a thigh.
Sure, it might be a mole, or even skin cancer.
Does it have an unusual colour or pattern?
Does it grow?
Please have it checked by a physician.