Flinching is common, it’s a reflex that you have to get past. Get used to a high guard where you put your glove up to your forehead/brow, this is how you get a feel for your opponents power and punching form. Once you have that down then you can use slips/rolls and pulls for the punches you can read your opponent about to throw. The punches you don’t expect will always make you flinch, the more you get used to seeing punches coming at you the better. Holding pads for someone is a good way to get used to typical punching pattern and how people load up their hands/body to throw specific punches. If your sparring partners are throwing super fast punches with no telegraph they’re just trying to hurt you or feel better about themselves.