If you dissect a flower to see all its inner workings, it may not look as beautiful to you anymore. If you spend all day, every day, with the person you love, you may eventually want to dissect them too. So when you're creating something, like writing a script, painting a landscape, or rehearsing your one-woman show over and over and over, there may come a time when you say, "If I ever see this piece of work again, it'll be too soon."
But to make something good, you need to spend time on it, creating it, adjusting it, and revising it. So how do you work on something without wanting to throw the damn thing out the window?
Add something to it- something that excites you. If you're bored with your script, add a dysfunctional character trait to your protagonist. If you're a painter, add a fluffy white cloud. Put something extra into your piece that gives the work (and you) a fresh look.
One time, before getting to work, over-caffeinate yourself, eat a whole bunch of sugar, or get a little drunk (note: I am not a doctor. If you have a heart condition, diabetes, alcoholism, or you just can't be trusted with any type of mood-altering substance, then don't do this.) I'm not saying do this every time, just once. See if it stimulates something creative in your work. This may totally not work, and could backfire in your creativity, your romantic life, or could leave you crying in a pile on the floor by the end of the day. But hey, you're not working anyway, so you may as well try something weird!
Keep working on it, even if you don't want to. Don't be a big baby- get back to work.