Any 'big' event in my life makes me sick

Hello

I'm not really sure in which category to post, it could be a agoraphobia, or social anxiety..
Basically, a lot of things that happen in my life just make me nauseous. This is a feeling that can remain with me for days, or even months.

It first started when I had a girlfriend: we were a happy couple, never had any problems, shared the same opinions about most things, we were a good fit.
But suddenly after a few months, I got sick in the morning. I stell went to school, were my girlfriend was, but it was very hard for me because I felt nauseous and dizzy the whole day.
After a week or two, this feeling of sickness went away. We thought it was just the stomach flu or something like that. But in the following period I had that 'stomach flu' about 4 times in one year.
Sometimes it went away in a couple of days, sometimes weeks or even months.

I was going on vacation with her, and litterally three days before we were supposed to go, I got sick, just nausea and throwing up, but I went anyway. I was sick on vacation for about 5 days, I lost
a ton of weight and felt so weak.
When we got back from vacation, and she asked me to come over, I just magically got sick, again for more then a week. And I have had many periods when I was with her, I just had to go back to my home because it always made me sick.
It got to the point where she would call me to do something together, and I immediately got sick.
It was impossible to live like that and I eventually broke up with her, after almost 1.5 years.

It was more than half a year ago, I'm over the breakup. She moved on, I moved on. But the sickness didn't.
There have been a lot of important occasions since then, like going to university for the first time, where I just got the same nauseous feeling.
When I go out with friends, I sometimes get sick too. And sometimes I just go home, and on my way home, I always start to feel better.

It must be anxiety! But what is going on?

When friends ask me to go out, i'm afraid to go because I don't want to get sick.
I'm afraid to start relationships because I don't want to get sick.
I can't plan anything big, like going on vacation with friends because... well you've got, I think :)

Thinking about the sickness, is probably the trigger I think? But I can't not think about it anymore..
Please help me! Life could be so much more pleasant if I haven't been anxious for all this time.