i didnt have this problem but a few others have. Rest assured its the combination of excitement and nerves!
Mint is very good in relieving nausea, so take some peppermint/spearmint lollies to suck on.
As 27mm said, always have breakfast and something sugary throught the day to keep you normal. Perhaps take some peppermint tea too?
You should be fine by your 3rd, 4th flight so dont worry too much. Alot of people are ill in their first week (vomiting ill) and some (eg: me) ended up with constant ear trouble for the first year instead. Rather take the
anyday!
Have fun!!!