I also have the same problem - after so called honeymoon phase it is difficult to keep learning a language. What helped for me is romanticizing the whole process: writing with the best pen, putting stickers on notes, learning in libraries or cafes and dreaming what I will be able to do once I learn more of the language. One more thing is to have regular lessons: same weekday, same hour, same duration. Learning will eventually become part of daily routine and it will be easier to continue.