@Tennis_Fever
I have been through similar situations , but without the scorelines.
You need to be less result focussed in these circumstances , and try to view the game , and how you are playing more objectively - who is doing what to who in the points? why is x y or z happening, are there any patterns or trends occuring?
If you feel you are making good decisions on court and in points then you have nothing to worry about, if you are fully commiting to your shots , and not making daft errors, or your opponent just plays better. Mentally you need to cut yourself some slack.
Confidence is a very fluid feeling an emotion, and some players (myself included) can find their performance varies massively around this.
Just reading what you have put , it reads like those couple of 0 sets have really knocked you mentally, when there is no need to have such a drastic reaction, just look at the amount of 6-0 sets in the pro level game, and take comfort there.
Try to play on a point by point basis, focus 100% on playing your best in that point, in that moment! , commit to the shots needed, and concentration needed for each point.
Give yourself praise when you hit a good shot or win a long point etc. Let the score take care of itself, as when you are feeling fragile it can often be a distratction.
Become 100% emotionally invested in each single point, and dont focus so much on the big picture, re-build the foundations of your confidence, and play to focus on re discovering your style and way of playing, as more than likely you have stopped doing things you normally do well, and are playing with fear of losing, rather than for enjoyment. Winning/losing is by product of all these small factors.
You cant just switch on confidence mode. However if you think of your confidence of a wall, you can break it down , and be gone quickly, mostly by your own thoughts or self damage.
By using some of these steps and more, you can rebuild the wall brick by brick, and hopefully learn more about yourself in the process, to stop this happening so severely next time.
Another quick non mental tip, that i found to help, is to work on your B game. When you have an A game that is not working , you need to have a good standard B game that is still good enough to win matches or be competitive , rather than more of an all or nothing approach.