Extreme nausea!

Okay so I'm not naive, I know I'm going to throw up at 6 weeks pregnant. However, I've never had this problem with a pregnancy & I've had 3. Everything I eat literally comes right back up. For example: I took a bite of mashed patatoes & less than 5 seconds after swallowing it came right back up. This has happened 5 times now! Water, ginger ale, crackers, nothing will stay down! I have no idea what to do. Some experienced mamas please help!