Hi needhelpasap and welcome to the forum. I'm very sorry but Indyfishy is right, your betta has a tumor. There isn't much you can do under these circumstances short of having a veterinarian remove it, a stressful surgery that the betta may not live through. Definitely continue with the epsom salt, which will help with the swelling and pick up the API Stress Coat as Indyfishy suggests. If, at any time, he begins to be in distress, then you may need to consider doing what's best for him. If it comes to that, please post back. We're all willing to help you make the best decision possible and we'll be here to support you.
Hang in there and keep us updated.