If you still feel horrendous after 7 months and being on 100mg, then you need to go back and speak to your GP.
The first 4 - 8 weeks can be horrendous, but it should have settled by now.
It sounds like you need them or something to help your depression or anxiety, so you need to change the mentality of thinking you can deal with your problems without them - Because you clearly can't and it's ok to admit that. Thousands of us are on them for one reason or another.
Go back to your GP, speak to them. It's what they are there for.
PS - From experience, once you have something like Sertraline in your system, its very hard to deal with coming off them. Even if you slowly come off. I was on them for 2 years, they worked wonders - I then spent 6 months gradually coming off because I felt like I didnt need them. A few months later I was a mess! Now on them for a 2nd time and they dont seem to be working as well as they once did.
So I have mixed opionions about it. But if you have started taking them, do not come off them until you speak to your GP. And certainly dont just stop taking them as you will certainly be in for a rough time.