I am very sorry to hear that you suffer from such severe motion sickness. The good news is that, if you have suffered from this for your entire life, then it is unlikely to be a serious medical problem. The bad news is that, if it has not gotten better by the time you are in your 30s, it is likely to continue being a problem for you for the rest of your life.
We do not really understand what causes motion sickness. There is no obvious problem in the brain or motion sensing apparatus of people who have motion sickness, which suggest that the problem has more to do with how individual people subjectively experience motion.
Unfortunately, there are no curative treatments that can fix motion sickness once and for all. Controlling symptoms when you know you are going to be in a situation that brings on the symptoms is the best you can do. There are numerous popular remedies for motion sickness, such as pressure wrist bands and ginger, which may be of some help. Also your primary care doctor
can prescribed several different medications for you that you can take to prevent symptoms on an as needed basis.