I have had small painless lumps under my armpit, neck and back. Some I have tried to squeeze and out came a whitish, buttery oily stuff. What is it?

Epidermoid cyst. It sounds like epidermoid cyst. It is usually just bothersome but not dangerous/cancerous. They usually continue to recur. Consuming a diet low in carbs, milk and high in healthy fats (butter, olive oil. avocados, coconut) should help to reduce their size in a few months. Try warm soaks, application of tea tree oil. They may help too.