My Son, 11, new to Asthma

Hi folks, my son has had persistent rhinitis for 7years and it appears now to be changing into asthma although the GP says the tests have not been 'diagnostic'. He was on a brown inhaler for four weeks and as soon as we started taking him off, he got worse again.

He is being treated for asthma but does not have a diagnosis. Any advice as to my next steps would be gratefully received.