This is something I've been struggling with since I've returned to scuba diving. I posted about it not to long ago. And, before and since that post, I've done extensive research trying to find a solution. I'll try to share some of that here.
As @emoriera pointed out, having your weight belt or waist band on your BCD too tight may be contributing to your problems. I think it may have been a small factor in my own illness but, I don't think in my case it was entirely responsible.
Another possible cause may be Hypercapnia. If you have a habit of skip breathing or don't fully exhale while breathing, it can result in excess carbon dioxide in your blood which can result in nausea. At one time, I thought this might be the source of my problems so, I tried working on my breathing. It didn't seem to help me very much but, it may help you.
For me, I became nauseated during my very first pool session. I also vomited several times during my OW check-out dives while in a protected lagoon (i.e. no waves, no surge). I became violently ill during my first boat dive (primarily due to a strong surge I think). And, I've become nauseated several times while diving in quarries (again, no waves and no surge).
I've been prone to motion sickness all my life. However, when I first started diving many years ago, I did not become ill while diving when there were no waves and no surge. I've come to the conclusion that, over the years, I've developed an even higher sensitivity to motion that I had when I was younger. Apparently, for me, just the sensation of near weightlessness while diving is now enough to cause motion sickness. Even though there is little to no motion involved.
When I was in the Navy, I found that the ONLY thing that helped my motion sickness was Scopolamine patches. During a recent trip to Pensacola, I got the opportunity to once again try the patches to alleviate my motion sickness. I put a patch on the night before our first dives and covered it with a waterproof Band-Aid. Over a three day period, we did three off-shore dives and two spring dives and I never once felt the slightest bit nauseated.
So, I now know that I have something that will work for me. The problem is that I often dive at quarries on the weekend and I may go and only get one dive in. And, I hate to waste a patch for just one dive. So, I've been looking for oral medication that I can take before diving areas without a lot of motion. Meclizine Hydrochloride (Bonine) and Dimenhydrinate (Dramamine) have proven ineffective for me.
It's my understanding that many folks who have not been helped by Bonine or Dramamine, have had great success with Cyclizine Hydrochloride. Cyclizine Hydrochloride (50mg) used to be marketed many years ago under the brand name Marzine and Marezine and was available OTC. However, it was banned OTC (supposedly) in the US because it is a "potentiator" and folks were taking with opiates to achieve a high similar to heroin. Anyway, Cyclizine Hydrochloride in the 50mg dose is still available in the UK, Denmark, Norway, Finland, and Taiwan (possibly others). Oddly enough, here in the US, the active ingredient in Bonine is Meclizine Hydrochloride but, the active ingredient in Bonine for Kids is 25mg of Cyclizine Hydrochloride (unless they've changed that recently). So, the next test for me in oral medication will be two of the Bonine for Kids. So, if you've tried regular Bonine and Dramamine unsuccessfully, you may want to give Bonine for Kids a try.
Also, some folks have used Zofran successfully. However, while Zofran is for nausea and vomiting (often prescribed after surgery or during chemotherapy), it is not recommended for motion sickness.
Sorry about the length of this post. Not trying to highjack this thread. Just trying to offer the OP some options based on what I'm currently experiencing.
Hope this helps.
