OP I am torn between thinking you are making this up and being very worried.
You said you are not making it up so I will go with the second.
I was bulimic for a few years. I was in my teens and I was thin. It isnt always a weight thing but a control thing or other reasons.
Even then, as a teenager I knew it was not normal.
You said that once you tried not to throw up and felt awful and tearful. This would be me every time, I dont want to eat the junk but I do then I try not to vomit but the calories then I would be sick and start again in a couple of days.
You have an eating disorder. It is very surprising that you dont think you have it. Because usually bulimics vomit and eat in secret. You have kept this from your sis for years so i take it you make ypurself sick in secret hence you must know it is not normal.
Now, it is normal to deny the disorder but in an anonymous forum You would be open an admit.
You think it is normal because you have done it for years
No. People dont do that. You can have a treat and we all feel a but guilty about it but making yourself sick is not what people do.
Yes, you go to GP and say exactly that.
It is not just your teeth (my enamel is fucked up now) it is also the acids on your esophagus thay can cause pretty nasty illnesses in the future, including throat cancer.
I dont want to scare you but that helped me, being informed