Always feel sick during the bike?

Could it be the combo of the swim and bike? You said it only happens on tris and not on your regular bike rides, so I'm just using process of elimination here.

Maybe you can do a mini brick with a pool swim, then hop on a bike to see?

I used to get 'motion sickness' after the swim, for about 15 or so minutes to get back to normal and I found out it was either because I was getting water in my ears or it was too cold for my head, but after I put on a cap and wore ear plugs, it went away.

Laura, you say that you have a bagel with peanut butter for breakfast before a tri.  You do your swim then jump on the bike and feel sick around the end of the ride.  Do you have anything to drink between breakfast and the end of that bike ride?  If I don't drink every once in awhile, I get that nauseous feeling in the pit of my stomach.  I take it that you are referring to sprint tri's so that would be what?  40/50 minutes of physical activity without water?  That would be enough to dehydrate you and cause the symptoms you mention.