I've had what you feel right now many times...To the point where I've thought I had a heart issue, pulmonary embolism, and a whole bunch of different diseases. You're right, it feels painful and weird to breathe because you're forcing it out unnaturally.
Unfortunately, I only have a few tips that have worked for me. One is to get my mind off of it in one way or another, and the feeling will go away, I promise you. Sadly, that's not so easy to do. The other two things is to meditate or to do some breathing exercises. Something that helps me sometimes is to eat lol, idk why.
I hope you feel better and don't let your thoughts get to you, its "just" anxiety that is making you feel like this when you breathe.