I think by the variety of 'cures' posted that you can see that it is pretty individual as to what works for who...
Some ex-navy/forces people that I know reckon that everyone
gets sea sick, if you haven't been, then it is because you haven't been in the sea state/situation that sets you off yet!
Not nice though.
I go sea fishing regularly, and it is at anchor or drifting when not under power when people start to suffer. Most are ok if they concentrate on the horizon and all the normal things. But if it is your time, then it is gonna happen.
Or charter skipper made me laugh last time we were out when he offered a cast iron cure for sea sickness to the couple of guys that were suffering:
'Stand under a tree'
Seriously though, if you can take the helm or concentrate on some task that makes you look out of the boat then you will feel better. Don't get your head down doing chartwork or loads of tide calcuations, because that really can stuff you up on a small boat!
You'll find something that works for you, just don't give up.