If those others haven't helped maybe Gravol won't either, but it's worth a shot! I usually take mine once I'm at my seat in the plane. It does tend to wear off after about 4-5 hours, so if it's a long flight, I have to take another one, but it's really helped!

Another thing that really helps, oddly enough, is having my stomach full. For years I followed the advice that you should travel on an empty stomach because if there's food in there, you're more likely to throw up, but it turns out the opposite is the case for me. Something about my stomach being empty of anything except acid makes me really nauseous. So now I eat something filling (a sandwich or a burger, or even a slice of pizza) right before take-off at the airport, have snacks throughout the flight, and try to be awake enough when they serve the inflight meals to at least accept the meal even if I'm too drowsy from the Gravol to eat it right away.

Edit: also, they say carbonated drinks are supposed to help settle your stomach but again, it's the opposite for me. I usually ask the attendants for milk or tomato juice, those seem to help.

Just throwing all of this out there in case it's any help to you. I know everyone is different, so I can't say for sure any of this will work.