I think if you are having a hard time breathing, you may consider going to the ER since there wont be much more things to consider at this point. They may supplement you with oxygen and consider a dose of intravenous steroids. Unfortunately with the nebulizer and long acting advair on board, not much more to do except get medical attention.
Yes, the fact that you are getting tired due to your increased respiratory effort is worrisome. If you have not had a nebulizer in the last hour or 2, have another one. Without examining you and seeing what your respiratory effort looks like, I would say just get to the ER as soon as you can. If you feel very ill, call 911 and that way the paramedics can give you oxygen on your way over there.