Hi Holly,
I hear what you are saying. I wish I could say I've never experienced this, but I have. It's a "yuck" place to be in and I sincerely hope you don't stay there for long.

When I'm feeling bad about myself I know my thoughts are on the wrong path. What helps me is to take control of my thoughts. I make the conscious decision to say no to ALL negative thoughts and self doubt.
I then think about the value of every person and recognize that I am just as valuable as anyone else. I can't be wrong! A great question which helps me is, "What would you say to your best friend in this situation?"
Another thing that helps is to write down all the positive things about myself, especially in the area I'm struggling in. I also write down my intentions on what I really want and what I'm going to do about it.
We all go through some form of discomfort when we go through change in a positive direction. What really helps is to recognize it as a sign post to say we're moving into new territory. That's exactly what we want when we want change! Sometimes our discomfort is in adjusting to what is unfamiliar. Before long, it becomes familiar and we're ready to move on again.
Somehow it's empowering to create a strategy that moves me from where I'm uncomfortable to where I feel I really want to be.
Forgive me if this sounds like a broken record. It's just that it happens to work incredibly well for me. Sometimes the most powerful things are simple.