After four years of playing (or three - which is it?) you can’t remotely have reached a professional level, nor is it likely that you have realised your full potential. In other words, if you were to take lessons, you could still learn a lot. On the other hand, with so few years of experience I don’t think you will be able to improve substantially on your own.
I expect you already knew that (if not, the previous paragraph already answers your question) and clearly, it is possible to have a fulfilling life without piano lessons. That begs the question, what do you mean by “needing” piano lessons?
I assume you have a goal in mind, for which you may or may not need further lessons. The other answers sort of assume your goal would be to play the whole Moonlight sonata. I haven’t heard you play so it is impossible to say for sure, but from what you wrote I would find it highly unlikely you could play the third movement at a reasonable level without help of a teacher (even with I think you would still need to practice some other repertoire first). However, if you have a different goal in mind, we can’t answer your question without knowing what it is.
Is your goal to fulfil your pianistic potential or to keep improving? Continue with lessons. Is there a specific skill or piece you want to learn? Continue and tell your teacher. Are you having fun at the level you have already reached without desiring to improve at all? No point in continuing with the lessons without motivation. Anything else? Tell us and I or someone else can make a recommendation.
It is impossible to answer whether your “need” piano lessons (besides the useless answer “no, since you can survive without”) without you telling us your goal. However, in the end I think it’s irrelevant: it comes down to this: do you enjoy having piano lessons? If so, continue! After three or four years you are only at the beginning of the journey. If not, don’t; I don’t see any reason to continue with a hobby you don’t like doing.