Head to a local pharmacy and grab a bottle of Cinnarizina (Cinnarizine). It comes in many different mg pills (last we bought was 75mg pills) and we cut them in 1/4's. Recommended doses for sea sickness are all over the place from 10mg up to 30+. We settled on I guess about 20mg cutting them in 1/4 and if that didn't work we could go to cutting them in 1/2. Can't buy this in the USA but it's sold in Mexico and Canada. Last time we felt seasickness the owner of a local dive op told us to get it. It is also the official sea sickness pill of the Royal Navy. If it's good enough for them it's good enough for me. Others here will disagree and say their are far better patches and pills via prescription in the US but you aren't in the US and you need to find something that works on vaca that doesn't knock you out. Cinarizine works and it is cheap.
Oh, others here will commonly claim that Cinnarizine can case cancer, brain damage, seizures, and Lord knows what else. We've been taking them as needed on dive vaca's for years with no problem whatsoever. We aren't taking baths in the stuff or ingesting it daily for years. I'd rather take Cinnarizine and enjoy my diving than cutting dives short or risk hurling underwater with my reg out or through it at depth... Seen others do that... Lotsa fish show up out of nowhere... No interest in doing that personally.