Fentanyl is a very strong opiate, more than 50-80 x stronger than morphine and very addictive. Stronger than heroin. Definitely not something worth using, not at all appropriate for your condition. It doesn't even make you euphoric. For some people under severe post surgery pains it may serve as a relief under medical supervision.
Please understand that this is a serious and dangerous medicine for you to consider no matter how much alcohol you are using. And the fact that you don't know this makes it even worse.
There're are many other ways to deal with it. Search for medical help/assistance so that you can have something more appropriate prescribed to you. Some patients use benzos during the treatment. There are different meds and you can do this right under orientation.
A lot of people die using fentanyl. There's nothing good that could come out of this situation as you'll put your life and health in danger besides getting hands to something way worse than alcohol.
Most of us have gone through very serious addiction problems reason for which I'd strongly advise you to search for something more suitable to this situation. Besides I doubt that fentanyl would make you euphoric.
You'll just add something that will be much more difficult to deal with. There are different types of meds that can help you to go through this.
Good luck and keep and touch!
Erik