Hi there,
Choosing a discipline can be difficult and it really should be something you have a true interest in. Generally if you don't think you will enjoy the course then you will have a tough time finding the motivation to study and learn.
I'm not sure how much I agree with your findings on mechanical and civil engineering. While it may take a few years to get established and finding your speciality, I wouldn't say this is any different from any engineering or in fact a lot of career routes. I would also say that shifts are generally not on the weekends unless there is a specific task to be done such as a site visit which cannot be done between mon-fri. Generally I wouldn't put down civil/mechanical engineering as being unappreciated but I understand it may not be your passion.
Engineering degrees can be great as you don't have to follow an exact path. After studying one discipline you may find yourself working in another field anyway, the degrees don't tie you down to one field. It's more the experience which may point you in your direction.
If you have any universities you like in mind then I would recommend having a look at the courses they offer and the modules you'd do. See if there are any which call out to you as interesting and you think you may enjoy learning about.
You've said there arn't any careers which you have a passion for. This is normal and lots of people go to university doing what they like and then figure it out while there. It really should just be a field which sounds interesting to you and you think you would have fun doing. Keep in mind you are not going to love every aspect of the course. Every course will have its pros and cons for you, and you may have to slug through some of it to get to do what you really enjoy but it will be worth it!
Good luck with your decision,
- Sophie (uni of Bath)