difficulty breathing, keep needing to take a deep breath, is this anxiety or something worse?

Hi, i am male and 18 yrs old and for the past few months i have been having difficulty breathing, symptoms such as, the urge to take a deep breath, feels like when i breath i don't take enough air in and so i have to take a deep breath to satisfy it and even then it don't always work, i had this about 4-5 years ago and got really worried so i went to the hospital and they done chest x-rays and said everything was fine, they also made me blow into a tube thing that tests your lung strength and my lungs where fine they said, after that it sort of went for ages, but now its come back and it lasts near enough all day, but if i am outside with mates enjoying my self it rarely happens, it mostly happens when i am in doors not doing much or outside doing the same, i also smoke if that makes a difference, i have also had the feeling my heart misses a beat (best way to describe it) but this hardly happens. people have said its stress or anxiety but it don't feel like that at all, all though last September my girl friend had my baby aborted but at the time it didn't really affect me that much also i have just recently broke up with the girl in question so do you think that has anything to do with it? please give me some advice if you can, thank you. Marc