Not OK, especially since there is no good reason why one would want to do it. It won't work for birth control, and if you are doing it because of a revulsion over semen, get the guy to wear a condom! If you are doing it because, as Christine says, you have a smell you want to get rid of, go to the doc and get swabbed for BV or other possibilities, and get it treated. (Get your boyfriend treated too, if you have something that can be passes back and forth.) I recommend condoms for someone who does not like the feeling of semen being loose in the vagina.
Douching frequently upsets the natural flora in your vagina and can cause problems.
If you are douching because of odor, you may want to see your health care provider for testing. You should not have a bad odor and it can indicate an infection such as yeast or an STD...which douching will not help and may make worse.