Try soaking a cotton ball in baby oil and holding it around the earring back and the area on the post where it is stuck, for about 3-5 minutes. It’s a pain to hold, but it should loosen the back from the post enough that you can get it off the post.. You can also use tea tree oil, which has antibacterial properties.
If that doesn’t work, see a doctor. You don’t want to eventually get an infection in that ear hole because you can’t clean the earring post. Even if it costs, it’s worth it to your health.