While I agree with Sunny, I would like to add some things. You don't have to have a family history of asthma, or pets or smoking in the home to have asthma. My younger son was a severe asthmatic as a child. He coughed and coughed and coughed, had big circles under his eyes, and was totally exhausted from coughing and coughing all night, every night. He had some appetite changes because he was just so exhausted. Some meds can cause that too. It just took my son quite a while to get back to normal, and he was on albuterol, Ventolin, Intal, Beclovent, Prednisone, Aminophylline and who knows what else. We were lucky in that the pedi who was on call the day I finally dragged him in (I am a minimizer at heart!), had a subspecialty in asthma, and we switched then and there to that guy. Our original pedi wasn't happy, but too bad. The new one had my son in great shape, and the good news is, he DID outgrow it in later high school. I understand it could recur when he is in middle adulthood, but for now he isn't even on Singulair any more.
Maybe you need another pedi?
It wouldn't hurt to see a specialist at this point, especially if the pedi isn't looking into other possibilities. I am a mom too, if I hadn't gone with my gut as far as my son was concerned, he might have died. He had severe asthma issues as a little boy, I called the doc one night to tell him that he was having more problems, things didn't "seem right". The doc told me to give a neb and try to let my son sleep. I gave him the neb, my son looked worse and just didn't act like himself..I scooped him up, brought him to the hospital. He spent 6 days in on oxygen as well as a diagnosis of pneumonia which made his asthma much worse. The moral of this story...always go with your gut feeling.
You know your kid better than anyone, don't let a doc foo foo you if you think something more is up with him.
I hope that you get answers...Sunny