In the beginning, chose one thing and learn to do it well. If you're just starting to learn a programming language, it is not time to start learning other languages.

If your goal is to learn how to program then stick with C++ and SFML. It is a very good library that will teach you how a C++ library should work. Learning to use good libraries is a necessary step in learning how to make them yourself.

If you are not a programmer and you are looking to learn game design, then an Engine like Unity may be better. Keep in mind that there are no short cuts for this. Programming is hard. Making games is hard. Switching to Unity because C++ is too hard isn't going to solve the problem.

If C++ isn't too hard then stick with it. You have not mastered it yet. I promise.

It depends on what you goals are in the end, making games, learning programming, or some combination of both. There is also nothing that says you can't stick to one thing now and then make a change later. GMStudio is great for 2d games, while Unity is great for 3d games though it has done many 2d games as well. Many great games have been made without the use of such high level engines, similar to doing it the way you have started, C++ and a basic graphics lib just to get some things done for you.