Well the first step is to recognise the problem.....so you're on the way to recovery already! Definitely don't try and sort it out by yourself but enlist the help of your club's instructors and make sure they're full aware of your situation before flying. Longer term the solution generally seems to desensitize the body and to do that means identifying what the main issues are, identifying the likely cause and working with the instructors on how to best overcome it.
It may be that you have general motion sickness and I can reassure you, if this is that case, that it will go away with time - I used to be travel sick on ALL forms of transport - land, sea and air. I now fly aerobatics in a glider and don't feel sick (unless I've done several sorties in a row!).
It could be that you're G-sensitive (reduced-G sensitivity occurs in about one in a hundred people and your instructors should already have subtely check you out on this without you even realising it - that's why we throw in a gentle stall right at the beginning of your training and when you don't have your hands near the controls).
There's a few ways of making things a bit more tolerable as you build up your tolerence too - Don't fly in the middle of the day when it's thermic and instead fly in the morning or early evening. Check with the instructors about your cable break recovery too - whilst you need to briskly lower the nose, you should experience only reduced-G and not negative-G (if there's lumps of mud floating away and above you when you do a cable break recovery then you're being too vigorous!). When flying, look ahead towards the horizon - particularly when turning. Don't be tempted to look down the wing as you turn and definitely don't be looking sidewise as you enter or exit a turn or pull or push on the stick - your balance ssytem in the ears does not appreciate acceleration/deceleration forces and will quickly drop the hint by inducing nausea.
Drink plenty of water and, as mentioned elsewhere, don't fly on an empty or too full stomach.
Good luck and hang in there - it's worth it! (an active glider pilot and instructor)