About a year and a half ago I read a book I wish I had read a decade ago: Decision Making and the Will of God (by Garry Friesen). It's a thick book filled with a lot of heavy topics. If you're up for a long read, I highly recommend it. But just in case you need the Cliff notes version in modern English, that's what big sisters are for. :-)
In a nutshell, Mr. Friesen argues that instead of trying to figure out God's "personal will" for your life—in decisions like whom to marry, where to go to school, which car to buy and what career to chose—your time is much better spent figuring out what God's Word says on the subject, applying the wisdom God has given you, and then choosing whichever option you like best! And let me tell ya, this method of decision making brings so much freedom!
Let's look at each of those steps again:
1. Spend time really seeking out what the Bible has to say about the decision in front of you. If God's Word is clear on a subject (like not dating unbelievers, not working for someone who exploits the poor, etc.) then your decision is made for you. In the pages of the Bible, we also find verses that guide us to examine our motives in making a decision (like not putting any person, job, or accomplishment in the place God deserves in our life).
2. Do your homework. Research, pray, and ask people who are smarter or have a few grey hairs what they think!
3. If the Bible doesn't give a command or principle that directly speaks to your dilemma (in other words, you have a "nonmoral" decision to make), you're free to choose whichever option you want. Any decision you make that doesn't go against God's Word is okie-dokie with Him.
Now, let's apply this new decision-making technique to your situation, whether you should go to medical school or directly to Doctors Without Borders. I can't think of any Scriptures that address either one. They both sound like amazing opportunities. I would do some more homework, more praying, and more asking around. Think about your motivation behind each of those options, and ask God to reveal any areas of your heart that might be tainting your view. Then use that gorgeous head God has given you and make whichever decision you feel is wisest for this season of your life. Whatever you choose, allow God to grow you, stretch you and make you more like His Son along the journey!
Happy decision-making!