In my profession as an economics professor and through churches I have attended, I've been around a lot of people who want to "make a difference." They almost inevitably equate "making a difference" with "working for a government or a non-profit organization like a church that is dedicated, at least in part, to helping poor people." Rarely do I hear anyone say "I want to work in accounts receivable for a company that makes faucets--or worse, a company that just sells faucets and other sundries."
But here's the irony: I suspect that you will probably make a bigger, albeit harder to see, difference in the lives of many by working in accounts receivable for Amalgamated Faucets than you will on your two-week summer mission trip or in your career as a relief worker. First, I paraphrase my advisor John Nye and offer you this insight from Yoram Barzel's 1974 article "A Theory of Rationing By Waiting": it is very difficult to give away money in ways that actually benefit the objects of your charity (here's an old article in which I discussed better charity). You consume resources in order to make transfers, and you give people incentives to consume resources seeking to get transfers. It's possible that the entire value of the transfer gets consumed by people standing in line to get "free" stuff.
Cleanliness, while not necessarily next to Godliness, is at least a few more steps removed from filth and the associated disease transmission. One quick and easy way to improve the lives of the people around you is to make sure you wash your hands carefully after using the restroom. By helping the faucet company run a leaner operation, you can help them expand and improve their faucet offerings. This in turn helps people wash their hands carefully. This in turn reduces disease transmission. Reduced disease transmission means less tragedy and higher productivity. It might not seem like much, but congratulations: by helping Amalgamated Faucet produce more, better, and cheaper faucets, you're reducing the probability that someone, somewhere gets sick.
Is it romantic? No. Will people write books about you and give you humanitarian achievement awards? No. Will you be recognized in church? Sadly, almost certainly not. Shouldn't you follow your heart? You've been told to follow your heart, but note what the Bible says about the heart in Jeremiah 6:5: It is deceitful in all things, and desperately wicked. If you want to help poor people, don't follow your heart. Follow your comparative advantage.