I was in the exact same position as you not very long ago.
My first ppl lesson in a Tiger Moth made me feel a bit barfy and had it been longer the results would have been messy. I got worried and there was talk of it taking 5 hours to get over it, even that some people never get over it(but most do). 2 days later on my 2nd lesson I felt completely fine. 2 weeks after that, my 3rd lesson I also felt fine so I think Ive got over it and I only actually felt sick on my first lesson: it may go away sooner than you think. The main reasons for this seem to be:
- Looking out of the plane and forwards helps rather than in the aircraft all the time
-as you become less of a passenger and more of a pilot, as you fly the plane more you will feel less sick. For example some people are fine doing aeros but when they are a passenger to someone elses aeros they feel sick. Even if you arent doing much flying concentrate and pretend you are.
- Travel sickness tablets. On my first flight I took one. It didnt work at all. The next flight I took a different one and felt fine, however it could be because I had flown just 2 days before so got used to it. I used it the third time and felt ok so I will be using it for a while yet but I dont know if it is actually working, it might just be me getting used to it naturally as it didnt work on someone else. I just dont want to risk being sick again. Anyway you might want to give them a try. The good ones are called "Joyrides" and I got them in Boots. Make sure they dont make you drowsy(they say they might but they dont for me)
- Distance between flights. I think this is very important. If you have a flight a month you are giving yourself more time to get "unused" to flying and it will take more flights to get over it. If you had 2 or 3 a week you would get over it a lot quicker. Sometimes even experienced pilots who have been away from flying for a while feel sick when they come back to it.
- I have also been told it helps to not go flying on an empty stomach
Hope it gets better