Unless you are accepted into a cadetship you cannot become an Airline Pilot just by completing a degree program. Once you have your commercial license you must build experience and gradually work your way towards an airline job. This could take ten years or more and a degree will not fast track the process. Many people never make it.
To research your options, search for “cadetship”, “first job” and “going north” type threads. Also check out the Rex, Jetstar and Cathay Pacific websites for info on their cadetships. Talk to as many people as you can, but remember that some people will give you biased advice (both ways).
If I were in your position I would study my absolute hardest to be offered a spot in Medicine. Make it your single goal this year. You can deliberate all you like later on... Aviation will still be here in 12 months.
Good luck!