Why does this happen?
Any negative emotion simply means you are currently focused on something that is out of alignment with how the broader part of you is focused.
What can I do to fight them?
Who says you need to fight them?
Sounds to me like all that's happened is you've just found yourself another Focus Block Topic. :)
I know it's nice to get your manifestations but the thing is that once you get this one, you'll then want something else, and then something else, and then something else, and then...and so on.
You're never going to be in a place where you have everything you want so you might as well relax a bit about it :)
Life is always going to be bringing you new things to come into alignment with (i.e. more Focus Blocks Topics) no matter how hard you try to get it all perfect...that's what physical life is for - the generation of new desire...so don't be so hard on yourself for just being alive :)
In fact, the better way to judge how well you are doing is how many new desires (or Focus Blocks Topics) you are launching.
Yes, seriously.
The more new desires you have for things/experiences that haven't manifested yet, the more exciting and fulfilling your life will be as you align with them - those desires will be pulling a tremendous amount of life-energy through you making you feel more alive than you will have ever felt before.
Those newly-hatched desires will cause you to start seeing your life more and more as an adventure rather than a chore.
In time, you'll actually start to seek out new experiences because you'll know that, no matter what happens to you, your life is always under your control...and you'll start feeling invincible.
It's a bit of a paradox, I know, but in acknowledging you'll never get everything you want and enjoying your in-completeness, you'll actually be experiencing the greatest feelings of completeness that it is possible for anyone to experience.