It sounds like it is difficult for you to get some relief from these intense reactions. I’m not certain what is keeping you from being able to regulate your emotions, but I can tell you that there are people who know about such things and can help. Give your parents one more chance by asking if you could get a physical from your general physician or pediatrician. Parents will often respond better if they think it is something medical rather than emotional. Once you get an appointment ask to talk to the doctor alone and explain the reactions you have. If you can’t see the physician alone explain them anyway. Either way the physician will then be in a good position to talk with your parents about getting some therapy — or an evaluation with someone who can help.
If a physical isn’t possible talk to you high school guidance counselor. He or she can help come up with a plan to help.