What are some causes of two large bumps on your forehead?

Cysts ? This could represent sebaceous cysts orlipomas. If these are cosmetically disturbing it is best to see doctor for removal.
Large forehead bumps. Without knowing additional information or seeing the bumps, it is difficult to say what they are with certainty. Color, mobility under the skin, soft?, hard?, growing? Your overall health and any medical conditions influence what the most likely cause is. Sebaceous cyst, lipoma, osteoma, plasmacytoma, dermoid cyst or metastatic lesion from a cancer elsewhere in the body. See your pmd for a check.