I know many of us are more sensitive to drugs than most, so are better starting on a low dose and ‘easing’ it in. I remember taking 62.5mg (a quarter of a tablet) of Diamox three times a day. I upped the night-time dose to 125mg, as it was during the night that I suffered the most head/neck/eyes ‘raised intracranial pressure’ symptoms. The reduced day-time dose still had a beneficial effect without such noticeable side effects.
I believe Diamox is very short acting, so I’m wondering if the daytime nausea is actually being caused by your raised intracranial pressure, i.e. once your morning dose has ‘worn off’. So, as I suggest, I’d try experimenting with a lesser dose (62.5mg) more frequent (3 times a day) and see if it brings improvement.