I've had breathing diffculties for a year now?

My breathing difficulties started a year ago, I was on my own and it was almost like I had forgotten to breathe, then when I needed to I couldn't breathe at all and it really scared me. Since then, I can't breathe normally. I have to take big deep breathes sometimes to breathe properly, and sometimes I can't breathe properly even if I'm sat doing nothing, and I feel really uncomfortable.
I've had a chest xray and everythings fine, also an ECG scan and they said that was fine too. I'm not overweight and I doubt it is asthma, my doctor gave me an inhaler but it didn't really work.
I often feel dizzy with it, and they have said it might be anxiety but I'm not worried about anything - however, if I do get worried it makes my breathing worse anyway because I have a problem breathing in the first place.
What do you think it is?
I've had breathing diffculties for a year now?
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