I often got carsick when I was young and even now can't really go on a boat without serious medication! So although I've been maybe 8 hours as a passenger with a mate in Cessnas/Robins/Warriors I was still very worried about starting the PPL even though it was something I've wanted to do for ages.
I've now got a grand total of 3 hours in the logbook over 4 lessons. First lesson we went above low stratus for lesson 1 and I was absolutely fine for a full hour.
Second lesson we were doing getting the aircraft well out of trim then the instructor handing it back to me to sort it out. I was obviously doing well as he gave it massive nose-down trim and as he said "you have control" I wasn't ready for the big-time nose-down. That made my lunch head for the exit, but I managed to hold it together for another 5 mins or so before having to ask the instructor to land. He was very good and pointed out there's no logic in paying £2.50/minute for someone to talk at you when you aren't paying attention!
Third lesson was a very bumpy day in blue skies and a gust caught us and flipped us into 30-40 Deg of bank, mainly due to the fact I didn't actually have my feet on the rudder pedals - I removed them when the instructor was manouvering and didn't put them back on for my go !

Early landing again.
Forth lesson was absolutely fine.
My instructor has been quick to point out he used to suffer from sickness and still does as a passenger if he isn't careful. The mate who got me into it was actually sick during his skills test!
Bigears make some good points but I'd strongly advise the sensible eating - I actually have a ham sandwich and a banana more like 2 to 1.5 hours before flying time. I'm trying to find the balance between making sure I don't get hungry/low blood sugar before landing, but eating as far in as advance as I can get away with. It's also worth thinking of this even further ahead - if you go out on a bender or have a big fryup/chinese/indian the night before you may not be helping yourself.
I'd endorse the wrist bands, but I'm assuming when Bigears said to "take" sickness tablets he meant put them in the flight bag rather than to swallow some - I'd personally think carefully about having meds before flying. Avomine works a treat for me, but once I take one I'm out of it for a good number of hours and wouldn't drive let alone fly!
So the message here is loud and clear - if there's any way you can fight through it, things will get better - I don't know about you but I don't remember the last time I felt sick as a driver but still have to be careful as a passenger (particularly if the wife's driving

). As you get to do the flying and your body gets used to it I'm sure it will pass or at least you'll learn to cope.
Have a word with you instructor too. Was it a particularly "sporting" day as they call it on here weather-wise? If (s)he isn't sympathetic, then look for another instructor as plenty are.
Best of luck MightyDucks, and let us know how you get on.