You were shy for 5 years because of a tummy ache, yeah nothing weird I guess.
Sigh.. so you can complain about a massive splitting headache but someone that can suffer from intestinal issues can't have problems? Have you ever had something like that? It's bad. Your gut can do a lot of weird stuff to you where it effects you psychologically.
Imagine every time you went out you ended up getting that headache. Now think about how you'd interact with people. Sure, it'd be different, but imagine what it would do. You'd probably be short, lack patience, not want anyone to talk too loud or grating in your ear.... it'd have an adverse effect on your interactions with people.
And I wouldn't say I was shy, I was uneasy. Think of the last time you ate sooo much your fucking stomach felt like it was going to bust through your pants, or a time you had immense gas and it hurt your stomach. Now think about wearing jeans and being out and you eat 1 slice of pizza, or a small appetizer , or fuck anything, 1 beer and suddenly you feel like your stomach is mad bloated, it's painful, you get uneasy..... yeah, that creates insecurity.