Help with product?

Okay, so I flat iron my (super thick, frizzy, curly/wavy) hair at least once a week, and I use serum on it. Can I do this? I need the serum, or some kind of product to protect from the heat a little. Two days ago I “washed” my hair with just conditioner, and today it feels nasty. Like a cheap wig with a film on it. Is it because of the serum of me?