Anxiety Support Group
Anxiety is a physical condition marked by intense and persistent feelings of distress, fear, angst or dread. General anxiety caused by routine day-to-day stresses usually passes quickly and is experienced by almost everyone at one time or another. However, such feelings that linger over time and are very difficult to cope with, and which lack a clear cause, may indicate...

The thing is, anyone who tells you that you're making it up in your head must be a pretty fortunate individual, because they clearly do not live with anxiety. This is ignorance, or denial. The good part is, we can fix both of those things by helping you to educate the people in your life. At least then, you can have a better idea of who is willing to help you and stick it out with you, and who will continue to be willfully ignorant.
I've found this site to be helpful in explaining anxiety and giving us the tools to help others understand what we're going through:
https://www.anxietycentre.com/anxiety/anxiety-101.shtml
And there are many other resources that you can find. You could even show people multiple books, websites, and even posts on support groups like this one to show them that you're not alone in this, that many people experience it, and it's hardly something you're making up.
That attitude is so hurtful to people like us because it completely dismisses our struggles and makes us feel as though we can't talk about it, or reach out for help, for fear of being told we're just making it up and being brushed off. I'm sorry people are doing this to you. I know how you feel.
Believe me, I know how you feel.
I hope you can find some understanding in your life, or at least here, if nowhere else. Always here if you need to talk.