If you put essential oil of peppermint (like 1/2 a drop) on the back of your tongue, it will help your body absorb more oxygen. I don't know that it will actually help your breathing, but it's worth a shot. I had some breathing problems around the holidays (I think it was going in all those stores) and that helped.
I had mild asthma when I was 12-14 (approx). Most of the time there weren't any symptoms or problems, but sometimes I would wheeze. The air capacity of the lungs is diminished, so I wasn't very good at blowing out BUT I could FEEL that I couldn't breathe in completely.
Do you eat dairy products? If you do, I would recommend you go off them completely for a while. They are closely linked with breathing problems.
The tea and coffee suggestions are worth trying, too (never heard of that but it's not hard to try and sounds reasonable).