Got a pimple on my chin, hard white stuff came out. Clear liquid, crust. Went away; one came in below it, now one on my butt cheek. What is this?

Sebaceous cysts. These sound like sebaceous cysts and occur when the duct leading from the sebaceous glands to the skin surface gets clogged with debris. The sebum "lubricates" the skin and when trapped dries forming the hard white matter you describe. It can occur anywhere you have a hair follicle. Good exfoliation can help prevent this. These also can be acne lesions, if bothered see a dermatologist.