Baby gagging himself

My son is 15 months old, the last 2-3 days he’s been sticking his fingers down his throat and gagging himself to the point of throwing up. No matter how many times I tell him no or take his hands out of his mouth, he keeps doing it. I’ve tried ignoring it and he just ends up throwing up. Does anyone have any ideas to help stop this or why he’s doing it? How can I correct this behavior?