As it turns out,I realised that, the field I'm working on is quite different than my original one. How to explain this current situation?
As someone who had to explain lack of progress numerous times to advisers and peers, I think you should not start with the negatives. Present succintly what you have succeeded to do. Even if it's not enough by your own standards, you should not say so. Leave the judgement to the adviser.
You should also tell them the parts where you have partial progress, and explain where you got stuck. Ask for advise on how to get unstuck and work more efficiently, if the adviser doesn't give you some advise himself. If there are things like your need for a place to go for work every day, which could positively impact your work, mention them to your adviser.
Having to learn the basics from scratch is not an easy job. Your supervisor is likely to understand that. They are also likely to understand that you needed some time to get re-accustomed to your field since you've been out of practice for a while. You can tell them that it took you a while to get into things.
I think you should be honest and help them make the best decision in what needs to be done to complete your project. At the same time, there is no need to expand excessively on your personal issues.