Ok, let's start with what is probably the main issue here, your perception of yourself.
You say that you are "increasingly depressed about" your scores, and then you go on to talk about "confidence." So it sounds as if you think your performance on the GMAT so far somehow indicates something essential about you.
That's just not right, and there is nothing to be depressed about. Want to be confident? Then see things for what they are. The real deal is that you are an infinitely capable being who could score 800 or 1000 or 100,000 on the GMAT were there such a possible score. You just haven't yet learned to play the game well enough yet to hit your score target. That's all.
It does not make sense to get depressed about your skill level. What is there to be depressed about? The only response to your scores that makes sense is to seek to increase your skill level and your scores in the GMAT game.
You said "Speed is an issue and that indicates my lack of practice."
So there is no mystery there. You just said it. You need more practice. Is that something to get depressed about, or would a better response be to, uh, practice more. I guess if you are not confident that you can hit your target, ever, then I could see why you might choose to get depressed rather than practice, but, as I already said, you can obviously hit your target. So the optimal course of action here becomes clear.
For quant practice, go to the GMAT section of
https://bellcurves.com/, set up a practice account, and hit every quant category in the question bank, at first doing questions slowly in order to insure that you learn how to do them with good form and get right answers. Then speed up, still seeking to get right answers. If you achieve an 80% or higher hit rate in every category there and you really learn how to get the right answers, you will pretty much be assured of hitting Q49-51.
If you want to work on DS specifically, you could practice using the Veritas Question Bank, which has a DS only category.
Practice, practice, practice.
I say use both question banks, working on DS and any other weak areas that you find. If doing that does not do it, then come back and we will give you some more ideas. At some point you can be sure all of it will add up and you will hit your target.
As far as SC goes, what's the nature of the problems you are having? Do you know rules or question building blocks and still not get the right answers? Do you feel that you don't know the basics? What you need to do to increase your SC hit rate depends on what's going on.
There are not so many rules to apply when doing RC questions. So for RC probably you need to get better at seeing details and really noticing what about answer choices makes sense and matches what's said in the passages, and what does not. Probably you need to get better at seeing the picture and the details of SC questions too.
For some great RC practice questions, once again the Veritas Question Bank is a good start. Just be sure to start off working slowly and really seeking to get right answers. You won't very easily develop skills or form by quickly burning through question after question. You are better off going slowly until you develop skill and form and then speeding up as makes sense.
So there are some ideas. Maybe you want some more detail on how to work on verbal. If so, maybe you could provide some more detail for people to consider in coming up with answers for you.
