What Causes Difficulty In Reaching Orgasm While On Contraceptive Pills?

I am unable to take combination pills due to excessive mood swings and bleeding. 2 months ago i was put on the mini pill, micronor. I have had normal periods and no mood swings, which is great. However i have found since being on this pill i am unable to reach orgasm during sex, which has never been a problem before. Could this be a side effect of the pill? Are there any other progesterone only pills that could solve this problem?