Asking for help is a good way to start. HN can sometimes be very harsh or critical, so I hope that you are happy with your responses.
If you are 19 then you are probably worried about disappointing users, parents, and other people. You need to understand something important, which I will give to you in a story. Think like you're a professional chef, and your kitchen gets overwhelmed: I will tell you, your customers will wait an hour for their food to come out, if that food is good. Obviously you don't want to make them wait an hour, obviously they will be impatiently staring at their watches, but all of that will be forgiven if what they're waiting for is good. Similarly, a good product will be much easier to sell, when you have time for it. So: if you start thinking of yourself as an adult and a professional, do not be afraid of making your clients wait. You have professional courtesy: they want your product, and they will wait, within reason.
If you want, universities make it very easy to take a year away from your studies: it's called a "leave of absence" in English. You can thus spend a year focusing on your tool without abandoning your studies, if you want.
If you really want to hire another developer, you may be able to borrow money, especially since you've proven that you're making money. Check out what banks will offer you in terms of loans.
You can do both at once, but you must be single-minded. If you want some inspiration, read the Water Book of the Book of Five Rings by Musashi -- it's freely available as public domain online. Pay attention to what he says about striking (cutting, in many translations): "When you wield your sword, your intent must be to strike the enemy. As you strike him your grip must remain, your hands must not flinch. Even if you parry the enemy's sword, only change your thumb and forefinger a little. Most importantly, you must hold the sword intent on striking the enemy. Your grip is the same in theory and practice: grip the sword as if you want to kill a man... Striking and slashing are two different things. However you strike, the act is decisive and resolute in your heart. Slashing is just touching the enemy. Even when slashing with vigor, even when the enemy dies, it is merely slashing. When you strike, your heart is resolved: you must learn to appreciate the difference. If you do slash the enemy's hands or legs, follow it up with a powerful strike. Slashing at heart is no different from touching with a sword. One who understands cannot tell the difference."
Similarly, if you want to make a dent in your work, you have to put your whole heart into the strike. You have to have the intent to destroy some bug, to get rid of some task, to finish some homework. It is very different from just investigative coding and meandering: it is singleminded and heartfelt. It comes with a certain joy/euphoria when it is over and you have made the change -- and this is addictive.
If you approach both your studies and your tool with singleminded intensity, you can do both at once. If you do not approach them this way, then work will pile up on one of them until you are overwhelmed by numbers.
If you already are overwhelmed by the amount of work, do not fear. Most people, especially teenagers, underestimate how much power patience and persistence have. A tiny river over time erodes a canyon; a sink will still drain, no matter the water flowing into it, if you can free up whatever is clogging it. Actually, this is the deep truth about how magic works: You say "how could that magician have known I would randomly draw the four of clubs," not letting yourself think that he or she might have simply taken 50 decks of cards, pulled out the four of clubs from all of them, and put them together into one deck, so that you had no choice. If someone can't see your patient actions, the results will be indistinguishable from magic.