Keep yourself hydrated as being de-hydrated can also cause nausea and sicky feeling (been there, PPL, thrown up
, instructor not happy
!!). Getting used to the new sensations of flying can be very weird.
You maybe getting anxious or nervous about your next flight, make sure you are well prepared for each lesson as doing this I found helped and also you have to get used to your spatial awareness, which can also be very odd, when you are in the air, .
Assymetricdrift has a few good ideas to combat this feeling, the mints helped me and I still chew on them now I fly commercially.
I'm 38 and not that active!!
Hope this helps.
M.