I haven’t told anyone that I am suffering from PTSD. But I want to seek help without telling my parents or anyone. What can I do
you can go and get diagnosed/treatment without needing someone else there with you, whatever your age. If you can, go to your doctor and have an open conversation :)
First and foremost - be glad that you have figured out the real problem.
If you are shy of reaching out specifically on it, atleast take steps towards remeditation e.g. stay with your family/group more often than earlier, avoid being alone, practice yoga/meditation/breathing exercises (however boring), sing your favorite songs more often (however bad a singer you are).
This shall pass and will provided you take the first step ie wear a mask and GO OUT!