Hi there noah, you're very brave for doing this first of all. I didn't have much trouble coming out to my family except my father. I had 0 hope that he would even accept it but he has and is still coming to terms with everything which is much better than what I had in mind. You're right, you can't hold it in any more and pretend to be something you're not.
My advice is to be prepared. Print out some information for them to read and if you can't bring yourself to telling them in person then a letter could work too. Do it at a time preferably when your parents aren't in a bad mood or whenever you feel most comfortable doing so. I think you should start out by saying how you'd really like to talk to them about something that's REALLY important to your health and well-being. Be gentle with your approach and try to steer away from saying things like "this is what's going to happen" or making statements about what you're going to do. If you're under age then you'll need to tell them that this is really affecting and hurting you. Ask them to be open-minded before the conversation starts and ask them to listen to what you have to say first. Make sure you have the information with you when you talk to them.
Only you know what to expect as you know them best but try not to set yourself up for disaster in terms of this. I came out to my Dad in the car on the way to one of my appointments with my psych and let me tell you... it was VERY nerve racking. He sort of went silent for a bit and said something along the lines of "Okay, I understand just go in for your appointment and we'll talk after". That whole time I was discussing it with my psych I was feeling extremely nervous about what was to come. I had her call him and he was saying how he's not mad and accepts it and that he still loves me. The drive back home wasn't too bad either. I couldn't believe his reaction at all and I can't stress that out enough. He's not as supportive as I'd like but it's better than nothing. Just know that anything could happen and no one can predict someone's reaction no matter how well you know them.
One more thing, do you have any siblings/friends or others you can trust to come out to first? I'm sure that'd be much easier and you could also get them to tag along and help you explain things to your parents.
Good luck, I really hope all goes well and that I was able to be of help!
