How can I resist junk food?

So I am 17 years old, and i have this slight (condition if i may call it?) where If i eat chocolate, candy, cheese, cupcakes, cake, etc (all that kind of junk food) I will become really nauseous for a LONG time and it well mess with my digestive system.

I haven't eaten junk food in about a month which is good for me but i was wondering how i could resist it in the future? Like if i go to lets say a birthday dinner, a party, an event, holidays, or any other special events where i see a bunch of my family and friends eating junk food like chips and cookies and all the stuff i absolutly love. I feel like it's going to be so hard and I'll be like the only one not enjoying the junk food at these gatherings. I can't eat pizza either. I kind of feel bad. Any suggestions?
How can I resist junk food?
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