Breathing problems caused by anxiety??

So I’ve been having this problem for a while now... over a year . I feel like I just can’t breathe right doctors have said it’s anxiety but can this be true when I feel like there’s nothing to feel anxious or worried or stressed about... I feel this ALL DAY, EVERY DAY! And I’m just so sick and scared and tired of it.. I wake up with it and go to sleep with it... I have started feeling pains in my chest on my left side too to my shoulder and the back of my shoulder when I stretch or something and they say it’s costochondritis... this just worries me even more and make me believe that having a breathing problem or trouble breathing all day every day can’t be because of anxiety.