I started my PhD thesis (in artificial intelligence and ecology) about a month ago, because it seemed like the perfect choice to continue from my master's degree. The problem is, since the beginning of the PhD, I started to become more and more anxious and have insomnia and depression-like symptoms (I will soon see a therapist for this reason). Now, I think of quitting PhD because it seems obvious to me that this new place does not fit me at all, and I cannot find enthusiasm for the work I have to do.
I feel very lost because my goal was always to become a scientist after finishing these last three years, but now I am pretty sure that this does not fit me. For the moment, my plans are to stick with the thesis for a few months to see if the situation gets better, but I don't have lots of hope.
So, I have a master's degree, I do something that makes me feel depressed, and I have no idea what career choices I should do. I have been thinking of starting something completely new, which is scary but seems to be the only way...
Would you have any advice? Have you ever been in that type of situation?
Edit: thank you for you answers. I just want to clarify that I am not afraid or worried about not knowing/learning/understanding the subject. The work I have to do is clear to me. But I have the growing sensation of being trapped in it for the upcoming 3 years. I feel like this is not for me.