I used to do the same thing. always feeling like i needed to take a deep breath and when I did, it didn't help anything. so I would do it again. it sill didn't help. It was always happening at the stressful points in my life. Like when my father died when I was 16. and again when my mother started seroiusly dating some guy who I hated. Breathing like that is caused by anxiety or stress. the only way t fix it is to solve the problem or get over it. the reason you probably didn't notice it when moving around was because you weren't thinking about what was bothering you. and you also didn't have the problem when smoking pot was cause you probably weren't thinking about it, or were more relaxed with the situation.
I hope this helps.
Let us know what the doc. says!